EDIT 12-19-11: SAI 4 Mac 0.3, download link updated.
New version has a completely different Wine core for testing.
If you're having trouble launching it install XQuartz.
This is PaintTool SAI running on Mac OS X via a self contained Wine wrapper. I put this together and figured it'd be useful for some people here on dA. If you'd like to give it a try click the download link. Enjoy!
To install: Double click to unzip and drag PaintTool SAI4MAC.app to your Applications folder.
Known issues include no tablet pressure recognition, this is a limitation of Wine and X11, sorry.
Repeat: TABLET PRESSURE DOES NOT WORK AND WILL NEVER WORK.
Maximize may not always function but you can still drag the window to the desired size.
DISCLAIMER: If it's apparent that you didn't read the description before making a comment don't be surprised if your question goes unanswered.
Attention: Due to the massive influx of stupid comments from people that didn't read the description or bother to comprehend anything about this before commenting, I'll be taking this down by the years end as I'm tired of constantly having to respond to these people. I decided to leave this up since stupid comments en masse seemed to decline, enjoy.
I likely won't be making any new updates for future versions of OS X or bugfix releases, this may change but the future prospects aren't likely, current version works on Mountain Lion but you may need to get the XQuartz libraries installed.
does anyone know why the pen pressure doesn't work? I have the full version on my windows laptop but I want it on my mac as well for course work. It's sort of necessary that I have working pen pressure for a lot of my stylised drawings. Is it possible that those having this problem have not changed the pressure in the brush settings? (The scroller under the pen size)