I really like that my in-edit comments aren't lost. I've accidentally navigated away more than once, and when I go back it still has what I was writing.
I like the page showing the most recently updated threads - I often will go through the forums I want to hit, and then later just use that to show me what's been changing. I need to make sure that I don't just use it though - it's a good summary, but things can move down the list quite fast with how active we are.
I like the left hand layout - bigger avatar, less clutter.
This has a touch of a gripe but is overall positive - while I'm a bit sad to not have a threaded mode for replies grouped with comments I used to use, the new system is made much more friendly by defaulting to the first new comment of the thread.
I like the in-place editting.
And don't sell the speed short. When I hit save, realize I left in a typo, can hit edit, it immediately comes up, I make the change and save again, and it's been singletons of seconds. Oh, so nice.