I generally advise founders of web startups simply to ignore universities' supposed IP claims. If you're really worried, rewrite all the code; it will probably turn out better. But it's about 1000x more likely that founders will hose themselves by not delivering something users love than that they will and their university will then crush them with a lawsuit, so if you're going to worry about something, worry about the former.

Previous employers are another matter. They can be adversarial, so you want to be more careful about IP with them. But universities are not going to sue you about software IP. I can't think of a single case of that happening.