According to Gary Woodcock and Casey King writing in "develop" issue 12, the Component Manager has migrated from QuickTime to System 7.1, although it's still present in QuickTime 1.5 so that QuickTime can use it on older Systems. Components can be used independently of QuickTime starting with System 7.1. This provides a new way to do plug-in code and will be faster than Apple events.
The QuickTime-aware scrapbook which comes with QuickTime 1.5 still leaves stranded 'alis' (alias) records in the Scrapbook file when you paste a movie (or movie segment) into the scrapbook and later delete it. The buggy QuickTime-aware beta Scrapbook which came with QuickTime 1.0 did the same thing. I'm surprised it wasn't fixed. This isn't a major problem, since 'alis' objects are fairly small, and you only notice them in ResEdit, but it's annoying.
Users should also avoid copying a piece of a movie from a movie file on a removable volume and pasting it into the QuickTime-aware Scrapbook. If you do this, and the Scrapbook wishes to display the "frame" containing the movie, it will harass you to mount the needed volume. That's particularly annoying if you close the scrapbook with a movie as the current scrapbook frame, dismount the movie's volume, then later reopen the Scrapbook. That sequence led to the first time I've had my Mac eject a CD-ROM and ask for a different one. If you must copy movie snippets into the scrapbook from removable volumes, I suggest that you put them towards the end of the scrapbook and remember to select some other scrapbook frame before closing the scrapbook. The movies then won't trip you up as often. However, it is good, not bad, that the Scrapbook pastes movies by reference rather than by copying the whole thing... a few movies would quickly eat up the whole startup disk.
Apple says that movie playback performance from CD-ROM is much better in QuickTime 1.5 than in 1.0. They are NOT kidding... the difference is dramatic. On my IIci, I no longer feel the need to copy the movie from CD to hard disk before playing it. And that's with old movies, not ones compressed with QuickTime 1.5 's better compressor. Admittedly, some movies from the QuickTime 1.0 CD that recommend playing from a hard disk don't play correctly under QuickTime 1.5, although that may also be related to my old Apple CD drive.