I can't see the point in doing this. You will have to pay import duties and VAT and it is unlikely that you will get any (UK based) support if it goes wrong unless you pay for shipment back to US. There is always the risk of stuff getting damaged in transit so you will probably have to pay insurance against that. You would probably also have to buy a 240V power supply if the laptop is supplied with a 110V one. Laptops are pretty cheap in the UK at the moment. Just what is the advantage?
If I was to buy the laptop here in the UK, it'd cost £1400. In america, you can buy the same laptop for $1100 which is £672.10. If I use bundlebox, they'll charge me FedEx delivery rate of £55 and insurance for £20, and so it comes to £747.10. After I pay 0% import duty and 20% VAT, the total comes to £896.52. I just need to know their commission rate before making a decision. £500 is quite a big saving.
Edit: The laptop available in america is actually a newer version with an i7 sandybridge processor.
I almost forgot about this thread until bundlebox came up in another, anyway, their website states that they charge 15% commission of the value (minimum US$15) and then the postal charge on top: BundleBox shipping rates