Not sure what to say but I read this info somewhere else and it definitely did the trick on my machine. I guess everyone's machine is quirky in it's own way. Heh.No problems here on my iMac with SS and iTunes 7.3
If you're running ShapeShifter, you have to put iTunes into the exclude list. Then it will start right up as normal.
My iTunes wouldn't open either. I was sneaky and got iTunes to open via starting it in Front Row first. Of course, you don't want to do that all the time.
I added iTunes to the exclude list, started itunes, closed it, then took it off the exclude list, and now it opens just fine. So, you don't have to keep it on the exclude list, It's just some kind of glitch I guess.