I wrote this post on startups and business plans in my school's blog :
Glazer: I just told you what the problem is. Your market description and competitor section do not agree. Any market that is growing at the rate you describe is going to have competitors. Saying there is none convinces the VCs that either you did not do your work or that the market isn't really there. If you think it is indeed a new product with no competitors think about the substitutes. No one is going to believe you when you say there are no competitors. When there are no competitors there are no customers too.