I tried QT 7 and it sucked.
For starters everytime I tried to view the HD H.264 videos found at
http://www.apple.com/quicktime/guide/hd/ QT 7 would crash and XP would give me an error.
After checking my error logs in XP I found the entry pertaining to this and it always pointed to quicktime.qts.
Uninstalled and reinstalled and the same problem. I did a search for this problem and found other people having the same problem.
Also, embedded wavs on some sites sounded really messed up, all sorts of noise and choppiness which was never present with QT 6.
I also had the same problem with QT 7 hijacking my mp3 file associations and I unchecked them under mime setting and the file types tab and it still wanted to play my mp3 when clicking on them on a site.
The .png plugin was also crashing IE when displaying pages with .png files. I then went in and unchecked all image types under the mime settings. That problem went away.
Even so, I finally gave up up and uninstalled QT7 rebooted then wiped out all Apple and Quicktime folders from my computer.
I then found the QT 6.5.2 standalone installer
http://www.apple.com/support/downloads/quicktime652forwindows.html. I installed that and everything is back to normal.
My QT7 standalone installation was 62 megs when installed which personally I think is insane.
The QT 6.5.2 installation is 2.17 megs on my PC.
Only reason why I upgraded from 6 to 7 is I kept getting the update notification whenever I opened QT and I never had a problem when upgrading QT so I figured why not. I've since turned off the auto notification and unchecked everything under the mime setting except .wav and .mov files.
If you do a search you'll see many MAC and PC users are having problems with QT7.