First, an answer to B777UA:
The A330 will be used mostly for international services, starting with CDG and expanding to LGW, FCO, and other cities. There will be some domestic relocation flights (see below).
The 767s that the A330s will be replacing on their current int'l routes will first be used on new routes such as Manchester, reintroduction of Amsterdam, expanded frequencies to new destinations, and possible new destinations such as Zurich or Milan (the only things approved and confirmed are Manchester and AMS, Zurich and Milan are on the block but haven't been approved by the gov't, so don;t look for them anytime soon). As more A330s take over the Atlantic, then the 767s will be used on transcontinental markets such as PHL/PIT-LAX/SFO.
There is so much US Airways wants to do in Europe that for the time being they need every aircraft possible, so don't look for 767s regularly doing domestic runs for a few years, when the A330s become more common.
As for the argument about the domestic 767...
Right now there is only ONE domestic 767 flight, and that is one daily each direction PHL-CLT. This flight is for aircraft relocation. One aircraft operates CLT-LGW-PHL-CLT and repeat, while another operates CLT-PHL-LGW-CLT and repeat.
Look for similar things with the A330 in a year or so. The first few A330s (probably until early/mid 2001) will be used on routes from Philly.