Many of us at the time "thought up" web-based email access but didn't see it through to execution much less turn it into a business. It's the same for most successful software ideas. Sabeer's most valuable contribution to Hotmail's success was his commitment and drive to turn it into a business. I have had a head start on a number of ideas that turned into big payoffs for others who had more entrepreneurial drive and better execution than I, so my ability to come up with the idea before they independently had the same idea was no advantage in the long run.
This is a very old link, but i thought it might be interesting to those who might have missed it...