I bought an update to Sony Vegas 7 last week. It has some useful little features that make editing easier, otherwise it is not too much different from Vegas 6. One shortcoming I have noticed with Vegas 7 is that it will not allow me to delete audio tracks from the timeline without also deleting the video, as well. This makes it more difficult to substitute audio tracks without using a nesting technique. Otherwise, no complaints. If someone else who has installed Vegas 7 knows how to do this, let me know.
Just for information, Sony is currently offering the Vegas 7 upgrade bundled with DVD Architect 4 for a bargain price of $249. It is a "bargain" if you did not previously have a copy of the latter product.
Sony has already rolled out a 7b upgrade, which you will be prompted to download and install after the initial boxed disk install.
When you upgrade to Vegas 7, and work on a previously produced Vegas 6 .veg file, you can't reuse Vegas 6 on the same file. So, Vegas 7 is not backwards compatable. However, Vegas 7 does seem to load and render faster than Vegas 6. Vegas 7 also has improved snaping to the timeline, with visual indications that show when clips are properly aligned vertically and back-to-back clip placement, that alerts you to any small gaps in the timeline placement. I have found this most helpful. I have already uninstalled the old Vegas 6 from my system.