I've been a contractor in the UK for fourteen years now, I'd reached a kind of barrier where to earn any more money I'd have to become some kind of manager, going contracting enabled me to earn significantly more and stay in very technical, hands-on kind of roles.
The advantages are: money, freedom (you can watch the internal politics and enjoy them as a spectator), the chance to work with a lot of different people and in different companies, enabling you to pick up all kinds of skills. Chances are you'll find exceptional people you can learn from most plaes you go, and opportunities for mentoring others as well.
The disadvantages are: you can be out of work for a few weeks or months when your contract ends, depending on where you live and the kind of skills you have, this is especially true if you will be relying on agencies to provide you with work. Theoretically you'll have less job security than permanent employees, though you'll be a lot more experienced at interviewing for jobs. You'll have to get used to training yourself in new technologies and it can be hard to transition between technologies (I made a leap from mainframe C to C# by taking what was quite a low paid contract, purely for the experience)
If you go full time you've got to provide your own retirement fund, it can be hard work getting a mortgage (this is probably especially true now, you'd be seen as far too risky) and basically you have to make all your own financial arrangements. You'll also have additional expenses such as legal and accounting bills to pay.
(also bear in mind in the UK, the government and IR have been at war with contractors since 1999, google something called IR35, in a nutshell the government position is that most contractors aren't self employed at all, but employees of their clients and as such should pay employment taxes on the majority of their profit, obviosly contractors tend not to agree with this assessment. A group was setup in 1999, the Professional Contractor Group, to oppose the new regulations. You can find their site at www.pcg.org.uk, well worth joining if you do become a contractor)