Read these 3 books - Crossing the Chasm, Innovators Dilemma and Behind the Cloud.
The only barrier to entry you can create is to consistently build a great product.
You intentionally start small, because you will not be able to compete with an incumbent... because the incumbent is always going to go for the full solution.
Opportunity lives at the intersection of what people need tomorrow and can be just barely built today.
The IT model of the enterprise has become a lot more user lead.
Execute like there's no tomorrow, strategize like there will be.