This is a common question with people looking to buy a camcorder. The answers are the same for any electrical equipment, so here is the way I see it:
You will need to get another power supply (or voltage converter) as the American one will run on 110v and we are on 240v.
If it breaks down it is an expensive return to the USA to get it repaired as no UK supplier is likely to honour a US warrenty.
If customs catch you it will cost you for import duty and VAT. This may not be likely, but could happen. If sending away for repair then the chances are you will get caught for tax on its return to you. This tax can be charged at any time in the future, not just when its new.
Other than the power supply I doubt there are any differences between a US & UK version. If you are happy to take your chances with the above and can save a few £'s then why not give it a go.
Mark.