For Vegas 7b Sony posted a revision to the manual. I downloaded a demo of a program called "Doc Diff" that compares pdf files. The good news for those who printed the original manual is that other than a couple of whitespace adjustments and changing the revision date, Doc Diff only found one change in the manual:
In the user manual, page 157, the grey box at the top says refer to the audio tab on page 304 for more info about how to set the maximum db level for normalization. This was wrong. It now correctly refers to page 316.
The Doc Diff program doesn't compare graphics, so it's possible some of the illustrations might have changed. That could explain why the update is 300 KB larger.