Pros:Liberal Arts education - the US courses are broad and flexible. Whereas here you might apply for Maths, specialise in Pure Maths in year 2 and then do a dissertation and research project on Topology in year 3; the Americans often don't even apply for a specific course.
You turn up at the uni and sign up for courses e.g. beginner's Spanish, advanced Maths, remedial French etc. In the second year you then choose your 'major' but you can still do loads of other stuff alongside that. For example, a guy I know who went to Yale did Economics and Psychology alongside a few other cheeky modules here and there.
Recognition - The US dominates world league tables, and so whereas in the UK only Oxbridge, Imperial, UCL and LSE are known worldwide, in the US you have loads - Harvard, MIT, Stanford, Princeton, Caltech, Berkeley etc. That said, as I said before if you can make one of the top US unis you can make one of the top UK unis.
Cons:The cost - woooowwww it's absolutely *loads*. I think around £25,000 a year depending on the uni, which is ridiculous
*apparently* Americans save up for years and years to send their children to college. Unless you're going to Harvard it's really not worth it, and if you think you can go to Harvard you should just stick with Cambridge here for 1/5 the price
The application - applying from the UK is effort - you have to do SATs and other exams, 2 personal statements and it's a lot of fuss and bother alongside your UK UCAS application. The time spent applying to Harvard and Cambridge simultaneously could see you screw up both applications.
The country - are you really going to fit in? Just consider it, I'm not saying you won't.