not too long, but the concepts would be exactly the same... wouldn't it then become, "who owns the idea?"

There is no such legal concept, at least not in the United States. One can own an implementation of an idea, but not an idea. If you can implement the concepts in a novel way, you're fine.

(In agreement, just to express it another way): Patents on implementations can and do effectively limit idea reuse.

E.g. if the idea is "a web 2.0 flower box" making a second implementation is fine.

If the idea is a "web 2.0 flower box using this specific patented method of procedural generation" then you won't be able to recreate the same product again - at least not without moving to Europe where there are no software patents :)

I don't think that is the case. If you are willing to spend a few hundred dollars you can get legal counselling from a lawyer.

Also, if you are attending startup school, they might have half an hour talk from someone on legal issues and you could ask that person.