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 ...