Most startups that I run into forget the one basic question which will determine their fate - what is your marketing strategy? They get excited by some "revolutionary" idea and jump straight into building a killer website, hiring a team, raising money, etc.
No one will hear a tree falling in a forest - no one will come to a website, however great...unless there is a strong marketing effort to get traffic. And, basically, there are only three ways to get traffic:
1) SEM - you have to have a deep war chest and spend a lot on Google and Yahoo before you even know if it will work!
2) SEO - hard to do in US since all the top spots are taken; easier to do in India - it is a landgrab and good land is still available!!
3) Viral - IMHO, viral just happens and you look like a hero if it does - but you cannot count on it and it is almost impossible to make it happen on your own
That leaves B2B - one deal with a big portal and you are the next Google! This is obviously easier said than done. And, don't even think of a sales force unless you are selling a high value item that companies need
Now you see why so few startups survive :)