Places, the much touted improved bookmark system needs a lot of work to go into it yet. For starters, you cannot add, edit bookmarks (and live bookmarks) in Bon Echo. This creates a lot of problems for people like me who literally live off their bookmarks. Also, there is no way you can create a live bookmark for pages like 30Boxes which doesn't reference the rss file in their meta tags. Basically, if Bon Echo cannot recognise it, you cannot add it. Now that sucks!
The browser itself (as Alex said it) is rock solid. If you're worried about memory leaks, they're very few (none that I've noticed) in this one which means it has reduced my browser restarts and minimize-maximize routines (config.trim_on_minimize :P) to a bare minimum. My system specs are the bare minimum, so you'll get brilliant performance out of this baby! If you're worried about disabled incompatible extensions, I'll suggest you download MR Tech Local Install, which will allow you to change the maxversion of the extensions, and make them work with Bon Echo (works for all extensions). Very stable, and faster than the 126.96.36.199.
My Request from Firefox
I hope they are able to put some sort of tab resizing feature like Opera, which allows one to create cascaded on tiled tabs. Also, I miss the 'tab locking' feature from Opera. Something like that is invaluable for Gmail tabs, which should remain open. I have the habit of accidently clicking a link in Gmail, only to see the tab get reloaded, very irritating. Basically, a much more powerful implementation of tabs and bookmarks (with inbuilt tagging?) is my request from the Firefox team.
I'll suggest this over the current stable release, if you are as frustrated as I am with all the leaks and bloatedness feel to Fx 1.5*! Keep up the good work guys! You make the internet heaven! :)
[Update]: Old new, but just wanted to remind everyone that Firefox 2.0 Beta 1 is out on the 6th of July (Meeting Notes)
[Update]: Places has been pulled out of Firefox 2.0. (Article)