I work in a help desk role with four other people supporting a few hundred so I was waiting to pull the trigger for the latest version because I didn't want to lose my workhorse browser in action. But when I started reading about all of the new features I decided I'd dive right into the release candidate given that the headache of backing up profiles and such between upgrades seems to have gone away. Now that the updates to Firefox come automatically and only require a restart of the browser I figured there wasn't really a good reason to wait.
I'm very happy with this decision so far. I can't say for sure if it seems faster or not on this setup, but I *can* say for certain that the new features are quite welcome. Especially being able to filter the junk that pops up in the awesome bar with some simple characters. It finally gave me some motivation to properly tag and organize the menagerie of "Unsorted Bookmarks" in Places. I'm quite pleased with the result and I'm already saving a lot of time when revisiting resources related to the support work I do. The only feature that's still missing from the browser that I find myself wishing it has is an advanced interface for creating the smart folders other than the "Save" button in Places.
The long and short: If you hated the awesome bar before and turned it off, give it another shot in 3.5 and see if the new features make it bearable. Thumbs up Mozilla.