I bought a PB in May this year while on holiday in the US and brought it home to the UK, so:
Your iPod plug - at least the three prong part that seperates from the main power adaptor - will fit the PB power adaptor and you can safely use it. The supplied extension cord will only have a 2-prong US plug, but I read on another PB thread that any figure-8 shaped power lead will work. Alternatively you can buy a 3-prong adaptor to use with the supplied extension cord.
The standard 1 year Apple warranties are international, so if you buy a PB in the US and have a problem with it back in the UK you shouldn't have any problems getting it repaired. If you want to buy AppleCare buy it in the UK though.
You can get a £ sign on a US PB keyboard without remapping a key - in International Preferences set your input menu to British and this will replace the # key for a £ (shift+3). To get a # press alt+3 (or maybe ctl+3 ... I'm not on my PB at the moment but it's one of those key combinations). I haven't tried to get a Euro sign yet.
It's well worth buying a PB in the US. I bought a stock 12" combo drive, 1.33 GHz, 60GB, 256MB, and with the local sales tax paid about £950, a saving of £200. And it felt so good to walk into an Apple Store and say "One of those please." I also got a .Mac account for $69.95, Sims Making Magic for my daughter for $30, MoH Breakthrough for $30, Call of Duty for $40. Now I just have to pay the credit card bill 🙁
Obviously you have to take into account import duty and VAT if you declare it to UK customs on the way back in ...