Indeed one of the top-class movies of 2010- The Social Network...a must watch for entrepreneurs! Lots of (startup) lessons get conveyed thru it.
Idea does matter, but success is not just about the idea. Also no one is owner of an idea. It is the time to market of its implementation that matters. You cannot keep idea as a secret of course, since you've to get work done and those working on it need to know the functionality. The ConnectU founders had brilliant idea with them but had a couple of programmers before Mark who had worked and left half-way. On the other hand it was Mark who worked almost non-stop. When others were walking he was running, when other were partying he was coding! It is the fast and aggressive nature that comes contributed to huge success in a short time. Undoubtedly certain things take time to develop and come to market, but there are some other things which must come to market fast and hence grab the right time. Despite the fact that your product need not be first in market, the ones released first tend to gather more crowd because of its novelty!
There are times when your presence will matter even though you don't have real work on your plate. Had the CFO been with the company when company shifted its base, he wouldn't have taken aback with numerous surprises! It is not for being skeptical about your partner that you should maintain your presence!!
On legal front there are n number of lessons- do not keep anything orally, have it documented may it even be a short contract. Your signature holds tremendous weightage- do not sign anything blindly, read carefully before signing. Consider paying anyone in equity as the last option.
The creativity of thinking has to come into action. You'll have to come out of your (assumed)limitations which are mostly rooted in mind. Push your boundaries, dream, believe. So get cracking with your idea....