The simple rule for successful online apps
Technology is nice, but community is the secret.
Once a technology begins to catch on, copying that tech isn't particularly difficult, so a technology-only tool competition will likely race to a price of zero.
Once proprietary content begins to catch on, copying it isn't hard, and continuing to produce original material that's just as good is incredibly difficult.
On the other hand, an app that is at the center of a community creates two kinds of value, and does so for a long time to come.
Not just obvious community software like Facebook, but tools like Photoshop and Word--ones that work better when others use them too.
Software is magic because one more user is free. But online software is powerful because it works better when more people use it.
The internet is a connection machine.