Shariah, or Islamic Law is often deeply misunderstood outside the muslim
The idea of harshness as mentioned in wharfinger's writeup is quite misleading (no-offence meant to wharfinger, I am sure he was being earnest). The islamic ideal of justice is something comprehensive that everyone can rely on, in ANY area of life. This holistic approach is alien to societies that make a differentiation between religious/moral activites and statecraft, or criminal and civil courts. A muslim would view these distinctions as artificial and quite arbitrary. The purpose of a just society is to prevent crimes, and provide justice when they occur by helping the victims, and punishing the criminals.
Simplistic, yes. But also true.
Often times the Shariah is criticised by people on the basis of its punishments, yet they fail to show the complex, intricate, and rigorous process it provides for establishing proof only by examination of evidence before any judgement is reached. Processes that were observed by travellers from the west in the past and brought back to form the basis of the justice systems in place there now.
To sum up: Shariah is a set of rules that guide muslims through their lives, and sets out responsibilities and rights, duties and crimes, and remedies for society. It is designed for a different type of society in mind than the one in which most of its critics live, which must be understood inorder to avoid prejudice.
In response to some of the points raised about Sharia by the_quark:
punishments under Sharia: Again, there has been a misunderstanding. I didn't intend to justify the punishments of the Sharia as a code of law - it stands independently of any relativistic cultural judgements made on it. The point about the average Westerner is this: there is simply no need to justify anything about Sharia to him, as he doesn't accept the value system upon which it is based. Islamic justice is swift, rigorous, and compassionate. The reasons for this elude people until they realise that Sharia is used not just to mete out punishments for crimes, but to generate a complete, self contained society which is fully functional, with minimal crime, and maximum welfare for the whole population. For such a system to flourish, crime must be deterred. It works. Just ask the Saudi nationals, most of whom will tell you that their country is the safest and most pleasant on earth. They certainly don't feel oppressed, and as a believer in Sharia, neither do I.
Muslims and non-Muslims alike: the only people subject to sharia are those who are living in countries where it is the law. The law in this country has to treat everyone equally, and religion is a matter of personal choice, so regardless, if you are part of the Islamic society, enjoying it's benefits, putting up with it's annoyances then you deserve to be treated no differently to anyone else who is protected by the law. This is a principle found in all countries, not just Muslim ones. Why should non-muslims be exempt from the law? Because they don't like it? Does that mean I can stop paying taxes to the UK government, and start killing? Clearly not. You don't like the laws of your society? Move.
Adultery: punishment for adultery is incredibly harsh, for both parties. Islam's duty is to preserve the family, protect the children, maintain the honour and dignity of each individual who is sincere in their love. The reason for this harshness is partly due to the fact that Islam allows both men and women to divorce each other quite easily. In fact the procedure under Shariah is identical for each person (regardless of gender) and takes less than three months. So if a woman is genuinely in love with another man, then she can leave her husband and family relatively easily. Thus there is no excuse for adultery at all, it violates trust, and destroys the fabric of love and sincerity that holds the family together, and places the future of the children in jeopardy. The guilty party bears full responsibility, and under Islam an adulteress can only marry an adulterer (and vice versa). Of course as you may have guessed, if this is the case, then the punishment for adultery cannot be death, and it isn't.
Fornication is punished differently, but under Sharia it isn't a capital offense either. Please don't confuse the Taliban or Wahabi interpretation of Islamic law as Sharia. These are two very extreme countries, a better example might be seen in Malaysia which has a much more normal Islamic system. As for the man 'getting off scot free' in the age of DNA matching, and paternity testing I find it doubtful that any man would escape the net of justice if a woman can't. "The Islamic world is quite modern you know, they have roads, police, books, and EVERYTHING!"
Rights of Women: I recommend visiting a Muslim country. Women go about unescorted, especially shopping, and with other women as well. Faces are usually uncovered, cos it's normal Sharia, which encourages modesty in both sexes but not being buried in cloth. Women have the same rights under the law as men. Just ask anyone. Sharia encourages education of both genders. It certainly doesn't stop women from reading. The head of the Islamic family is the mother, and so she owns the man, if anyone is property, which they aren't. People are free to believe what they wish, but Sharia does demand something that western cultures don't: sincerity. You can believe what you wish, but under Shariah you cannot preach Atheism or Christianity for the same reason you don't inject yourself with poison. It is bad for you.