Looks like Apple has decided to fix my recent discovery (Using Quicktime 7 with Quicktime 6 Pro) as a bug. According to the Software Updater,
QuickTime 7.0.1 provides several important bug fixes, a security enhancement, and improved compatibility with Final Cut Studio. This update is recommended for all QuickTime 7 users. For detailed information on the security enhancement, please visit this website: http://www.info.apple.com/kbnum/n61798
Important Notice to QuickTime Pro Users – Installation of QuickTime 7 will disable the QuickTime Pro functionality in prior versions of QuickTime, such as QuickTime 5 or QuickTime 6. If you proceed with this installation, you must purchase a new QuickTime 7 Pro key to regain QuickTime Pro functionality. After installation, visit www.apple.com/quicktime to purchase a QuickTime 7 Pro key.
The problem, it seems is that some people are reporting problems with this new Quicktime update. Perhaps, Apple tried to meddle too much with the Quicktime Pro 6 and 5 keys disabling function, that it broke the current Quicktime 7 software?
UPDATE 06-09-05: After upgrading to 7.01, my Quicktime 6 Pro application still works. I guess that you need to make sure the Quicktime Player app is renamed to something else, before upgrading to 7.01.