When viewing MPG files online, I have many problems with Panter/QT7 that I did not have under Panther/QT6. For one thing, the movies don't start automatically like the used to, and for another, there are incredibly herky-jerky. The experience was a heck of a lot better under the previous setup. On this particular machine, I haven't upgraded to Tiger.
I guess the thing to do is compare performance of QT7 under Tiger to QT7 under Panther.