Still some bugs, but exactly what I've been looking for, and the developer is making quick progress. Like others, I'd really like for it to run automatically in the background and change the icon without opening iCal. The option to close iCal still doesn't work for me on my PowerPC, so I had to create an Automator workflow that opens this program and then closes iCal. I'll keep checking back - keep up the good work.

Also, is it just my screen, or are the fonts for the number different for the open and closed icons? More options would be great, like icons that still have the month when closed or that don't have any number when closed.