In my opinion, the A330 is definitely worth it. Much like a new car, there's just something about a new plane. USAirways has gone out of their way to make the 330 special. I flew the 330 from PHL to LGW in August, and I was favorably impressed. I flew in coach, but the seats were fantastic--very firm but still cushy. Menus were passed around for meals, even in coach. The PTVs have a greater selection of movies, music, TV shows, documentaries, games, etc. than you could ever exhaust in a 7 hour flight. The movies and shows can be paused, rewound, fast-forwarded however you choose. Another of my favorite things was the 'wings' on the headrest that will keep your head from flopping back and forth as you sleep--a nice touch!
Admittedly, I have not flown UA internationally, and I am a US fan, but one gets the feeling that US is supremely proud to have the A330 and seeks to make it an 'experience', not just a flight. I flew a 767 back to PIT, and it was simply another flight to me, not as special.
I'd be interested to hear your decision and how you make out.