Lots, but at the end of the day it shouldn't mean that nobody should build first.

that's why a lot of products fail. They are solving problems nobody has.

People who, unlike a successful drug dealer, actually want to use their own product? I agree that if you are someone with desires not shared by the rest of society, you should probably go and talk to people and see what they desire...but it's also quite possible to think of something you and maybe some of your friends would use and have that be the guiding force in development. The problem with asking other people whether they'd like it, well [insert apocryphal story about Henry Ford and people wanting faster horses].

It's not either-or, it can be a mix. But it's not beyond the capacity of some hackers to hack on something they care about and, at the same time, have it be something that others will care about, unless all they're doing is trying to make a quick buck in the startup rush.