The ten suggestions

There is a running joke among atheists, saying that if Moses had been more liberal he would have called the ten commandments the 'ten suggestions'.
Although a religious person probably can't produce any more than a wry grin about this, for an Atheist it is quite to the point. After all, if one doesn't accept the bible as a leading guide to moral issues, which atheists generally don't do with good reason, then these commandments are not binding. That is not to say that it is immoral to follow them, on the contrary. Some of the ten commandments fit very well within our view of norms and values: our society and economy would not work if it were legitimate to kill, steal and lie and such acts would consequently be practiced in abundance. That is not to say that we should look anywhere in the direction of holy scriptures for moral guidance, as the scriptures of the abrahamic monotheisms (Judaism, Christianity and Islam) are hundreds years old and not compatible with our society today.
The commandments to not steal, kill, lie or commit adultery are among the few rules in the old testament that make sense. It might have made sense at the time but there are a lot of rules in the old testament which we would consider barbaric nowadays.

let's have a look at a few of these here.

If anyone in the circle of your family or friends entices you to worship another God you must, according to Deuteronomy 13:6-10, surely put them to death by stoning.
If your son or daughter doesn't obey you, even after punishment, Deuteronomy 21:18-21 says you must bring them to the gates of the city and the kid must be stoned to death.
Homosexuals and transvestites are (surprise, surprise!) also to be stoned to death according to Leviticus 18:22-20:13 and Deuteronomy 22:5 respectively. Leviticus 20:27 prescribes the same fate to Magicians.
In Leviticus 20:15 we read that anyone who has sex with an animal shall be put to death, which is gruesome on it's own. The poor animal however is, after being raped, also to be put to death! Now where's the justice in that? In Deuteronomy 22:22-24 it says something similar about women: when a woman who is engaged to marry is raped in town, they are both to be stoned to death: the man for the rape and the woman for not crying for help! If the same happens on the countryside, we read in ongoing paragraphs, only the man is stoned because the woman's cries for help could have remained unheard. It's surely a logic unheard of in our times.
In Deuteronomy 22:13-20 we read that if you marry a woman and it appears she is not a virgin, you can ask a proof of virginity from the parents of the bride. If the proof is provided, you will be punished. Fair enough, you have made a fool of your in-laws, not very nice. But if the proof can not be provided that the woman is a virgin, she should be taken to her parents' house and be stoned to death. (This insistence on virginity is still strong among Muslims and some Christians although the punishment is not as severe among Christians.)
In Deuteronomy 23:10 it says that if you make male prisoners of war, you can put all of them to death. If there is a female POW, you can make her your wife and after a month of bereavement have sex with her. If she doesn't please you, you can send her away. (But because she is not a virgin anymore, she will be in trouble - see above.)

here are a few more absurd rules:
In Deuteronomy 23:1 it says that if a man has crushed testicles or his penis is cut off, he is not welcome to congregation.
If a man suspects his wife is cheating on him he can, whether this suspicion is true or not, take her to a priest who, according to numbers 5:13-28, mixes holy water with dust from the floor in a bowl. The wife will drink this mixture and if she had sex with another man her belly will swell and her sex organs will shrivel. Shrivel, for crying out loud!
And exodus 23:19 forbids us to boil a kid in it's mothers milk.. who does that kind of stuff anyway?

This list is by no means comprehensive but I think after reading the above you got the picture.
I do not wish to doubt the usefulness of the commandments at the time they were written, and whoever was at their source is beyond the scope of this subject so I will not attempt to a philosophy about that either. At the time, the society was ordered in a completely different way and a moral code was highly desirable. The fact that we frown upon laws as mentioned above doesn't mean people back then would find it as unacceptable as we do now: for would we accept such a code of moral in these days? Of course we should not. Although in Deuteronomy 29:19-20 it says that anyone who feels inclined to act on his own moral views shall meet the wrath of god, even today's Christians say they do not embrace this kind of conduct. What a relief.
The citations above are taken from the old testament that contains the ten commandments, which is mainly a foundation of the Jews but also relevant to the Christians. To what extent old testament scripture is relevant to Christians is open for debate, but surely they accept the ten commandments. But accepting one part of a scripture and not another leaves room for confusion and erroneous implementation of the scripture. I often hear from religious people that scriptures are 'open for interpretation' and 'one must read between the lines'. Again, this leads to confusion and erroneous implementation, the resulting misery of which we can see in Northern Ireland, the middle east, former Yugoslavia and all over history.
That's why any Atheist will reject these scriptures as a whole and seek refuge to another sort of moral framework. In spite of what it says in Deuteronomy 29:19-20 we must have our own moral compass, independent of scriptures.
In our time, the secular part of the ten commandments has been covered by national law and any country to my knowledge forbids theft and murder. But in a way, other parts of the ten commandments have actually been disabled by law:

I am the Lord your God
You shall have no other gods before me
You shall not make for yourself an idol
You shall not make wrongful use of the name of your God

These four commandments are in conflict with the right to freedom of religion we know today as a basic human right in the civilised world. The old testament on the contrary, punishes the infringement of these commandments with death: everybody must get stoned. It also punishes or condemns other things which are accepted and/or legal in our world like homosexuality, sex before marriage etc. Slavery on the other hand is accepted in old scriptures while we have abolished it because it's considered immoral. Clearly the discrepancy between moral set out in scriptures and our current moral is bigger than the similarities.
Despite what religious people sometimes claim, we wouldn't live in a brave new world if we all would stick to holy scriptures and canonical law, or even the ten commandments. The middle east is a living proof of that. The fact that the Quran is many centuries younger than the old testament doesn't make it any more contemporary.

Contemporary or not, there is another aspect to scripture that prevents an objectively thinking person to base his moral on such scriptures. If one accepts moral from scriptures one accepts these morals because they are handed down from their God, and what he says is true and good beyond the shadow of a doubt. So killing somebody or stealing from them is not wrong because harm is done to that person, but because it is written in the holy book. If it says in that book that we can kill somebody in certain exceptional situations (and in the bible there are many of such situations described, see above) then all of a sudden it's perfectly OK to kill even your mother or other loved ones. Or to blow yourself up in a crowded bus, or fly an aeroplane into the twin towers. Of course the latter isn't mentioned in the bible or the Quran, but aren't we told to read between the lines?

The conclusion can only be that old scriptures, holy or not, are inadequate as a moral guideline in our times. We cannot rely on it in managing and designing our lives and that of our children. It may well be that some part of these scriptures include ideas that are still valid in our time, but deliberating about which are and which aren't may take more time than abolishing them all together and build a new moral framework from the ground up. And this moral framework should not come from above but from among us. It should be based on a mutual respect for all living creatures including their opinions, desires and entitlements.