Danile - big decision! I can imagine how hard it would be for you to leave. It is never easy even when you're excited and totally gung-ho about it. Keep us updated!
Meesa - hope you get some rest and relaxation soon!
TC - I've been subconsciously mulling over your sitch with class and your blog post today brought it up in my mind again. I am just thinking out loud so don't take offense at anything - obviously I'm not there and our kids are totally different so take what you want and leave the rest!
So, why do you feel the need to keep trying? It seems to me that the energy you expend to take him there, discuss the watching vs participating, etc. is not worth it. I think that he is just not ready for a class, and you can just wait another 6 mos or a year or whatever. M. is obviously a well-adjusted, healthy kid with just a little different social pattern than those other 3-year-olds in the class, and that is fine. I have seen him interact with people he knows and he is obviously just fine. I wouldn't worry about it, and just forget it for a while. Just be very matter-of-fact, no blaming or extended discussion, just "we decided we're not going back to gymnastics class; since you don't want to do the actual activities it's just not worth the money and my time." And I mean really, truly no blame or anything, just a very simple explanation. To me personally, 3 tries is enough and you've done your job of letting him lead the way - he seems not ready, and time to move on.
And of course he is interested in class and school and buses and stuff - it seems every single 3-year-old I know is, especially if they're unschooled.
I think if you aren't ready to send him to preschool, don't do it. You can talk and read about it plenty without actually doing it. And when you are ready, he will probably be more ready for it, too.
Good luck - I know it's not so simple when you're living it!