I think good design is important.

But it seems to me that the hardest thing is getting users to use your product or service (especially repeatedly). In a sense, it's more of a behavioral/psychological problem.

Ideas are bad because they don't get users. The best design won't turn a bad idea into a good one.

The thing I find most interesting about these examples is that all of them (I believe) had a dedicated user base -- as well as fast growing one -- in the beginning.

People really wanted to use them from day one.