If you're going to do b2b you'll never be forced, it's just that nobody will be doing business with you and your circle of friends.
VC's and angels don't like it when you incorporate early because that means that you've probably done a whole bunch of homework already and thus are a tougher negotiator.
Not incorporating when running a company is a great way to get into a lot of trouble. Fixing a bad incorporation at a later state is costly (but it can be done).
As soon as you start dealing with money and responsibilities to outsiders you should incorporate.