I'm working on pushing Acorn 3.1 out, which includes a handful of new 10.7 features (native full screen support, autosave, versions), the ability to assign a color profile to an image, some small changes and of course bug fixes.
You can grab Acorn 3.1b1 from the latest builds page.
If you're on 10.7 I'd appreciate any feedback you have on the autosave + versions support (do you like it? dislike it? etc.). It seems to be such a small and easy change, but it might have big implications on your workflow. Email us at email@example.com if you have thoughts on it.
I've also added a pref for autosave under the Advanced pane if you end up hating it. (Adding prefs is such a wimpy thing to do- but I've restored balance in the universe by removing the "remember workspace" pref if you are on 10.7, and deferring to the system pref).
You've got to admit though, a the versions browser is pretty awesome: