I can't really say for sure, simply because there was no "ok, well, my company is dead" moment -- the company is still going, I'm just not really doing anything. I guess the closest thing was my first day at Matasano, and I was mostly just excited at that point. I miss doing the full-time startup thing, but not so much that I'd jump at the opportunity to do it again right now. I'm sure that I'll get the itch in ~3 years, though.
When I was finishing college I could not WAIT to get outta there -- what between homework, regular work, and just being plain TIRED of school. The day after I got my degree, I said "man I already miss school!"
How did you feel right after you left your "startup life?"