For me it's :
dress down Mon-Fri (although I didn't mind wearing suits)
having no boss!
the challenge, I think Don Bright said it well...
the freedom to do what ever the hell I want...ski,golf, whatever, any time any day
no commute is nice, not trying to find parking,...but I admit I do miss the office pal lunches...looking at the girl interns...flirting with the ladies downtown
and here's one more piece of motivation, not one I need, but maybe one day I'll be able to just have enough to pick one up...for a goof