No, I think it's a mad idea!
Here's why:
1. While Sony products are well-designed, and thus tend to have better aesthetic appeal than some other brands, they're over-priced in terms of what's actually inside them. (i.e. other brands offer similar specifications for lower prices).
2. If it's available in the USA, it's almost certainly available here. Forget about your local PC stores. Head to the nearest newsagent and pick up a copy of 'Computer Shopper', to see what's really available.
3. If you buy a laptop in the UK (or from anywhere else in the EU), and it develops a fault, your primary rights to get the problem resolved are with the trader, not with the manufacturer. You have no such rights if you purchase something from outside of the EU.
4. While most manufacturers will honour warranties worldwide, you might experience some difficulties making a warranty claim in the UK. (Even if your warranty was valid it would, typically, only be for one year. If you buy from within the UK, you have rights against the retailer, for 6 years)
5. Shipping and importations costs are likely to be high. Although there's no import duty on laptops, you need to remember that HMRC will charge you 17.5% VAT on both the price of the laptop and on the carriage charges. (There's also an additional �8 customs inspection fee to be paid).
6. You'd need to buy another charger unit. The charger which comes with an American laptop will be designed to work with 120V at 60Hz. UK sockets supply 230V at 50Hz.
7. Any pre-loaded software would be US versions. With some programs that's probably not important but it could lead to some difficulties.
8. A laptop from the USA would have a US keyboard. There are only minor difference from a UK one but you might still find it irritating at times.
Chris