"Scratch your own itch" is what engineers do. "Build what people want" is what entrepreneurs do. Very, very few people can do both well. Bill Gates and Mark Zuckerberg come to mind. Apple had one of each.
You're lucky if you're one or the other. Even luckier if you realize it and don't waste your time trying to be the other as well.
I just had an email exchange with Patio11, which inspired the thoughts in this blog post, so i thought maybe someone else here would find this interesting given his hero status around here :)