I've been working on Acorn 1.1 for a while now, and while it still doesn't do everything I want it to, I've decided to go ahead and just ship the sucker because there have been lots of important changes that I'd like people to be using right away. Of course, I'll have to have a little beta test first so folks can point out the obvious bugs that I've somehow missed. You can grab the beta from the latest builds page.
What's new? Lots of things! A web export window, polygon selection tool, "trim to edges" menu command, vector tool improvements, a new crop widget, menu commands to move layers around, a drop shadow filter for bitmap layers, Levels and Auto Levels (yay!), drag images out of the layers list (and into another app such as the Finder or Photoshop. Although I have no idea why you'd want to…), resize an image via a percentage, option-drag bitmap layers in the canvas and the layers list to duplicate them, a grid, and lots of bug fixes. Full release notes are available.
Acorn also uses lots less memory now because of changes in undo and it's faster in certain areas as well, especially on 10.5 thanks to Quartz GL.
There have been updates to the plugin SDK as well- including the ability to make your own brushes. I've also included a new sample smudge tool (props to Andy Finnell for his "How to implement smudge and stamp tools", which I stole the code for the plugin from).
Brad has also been working on Acorn's new wiki, adding tutorials and documentation which will be a ton of help for people new to bitmap editors.
And if you've found a bug or have other feedback, make sure to use the bug reporting tool under the Help menu in Acorn.