I'm in the same situation. Have my US PS3, and my US A/V receiver and speakers, ready to set up this weekend.
I've ordered a new UK power cord for the PS3, and a 1500W transformer for the receiver (and my subwoofer).
My understanding is that, even though American PS3s say "120V" on the outside, the actual power supply is the same in every version. I guess they don't print 120-240V on the outside to dissuade Brits from buying them much cheaper in America?
I also understand that, if you're using HDMI cables to connect everything, there won't be any compatibility issues with the video signals. So you can plug a Sky cable box into an American A/V receiver, and then run another HDMI cable from the receiver to a British TV, and everything should work fine. The only issue is with using an American TV in the UK, because the actual tuner that decodes the video signal won't be able to decode PAL signals. If you use a cable box, that does the decoding.
Anybody know for sure that this isn't right?