I agree strongly with this comment.
There's such a thing as releasing too early. If the idea is not fully developed, and or its architectural ramifications still being explored, releasing early can trap you and make it far more difficult to evolve your concept.
If you're absolutely sure of what you're doing, what you want it to look like, how it will work, and you're just building gradually towards this well-defined final goal - great, release early and get users on board.
But if you're not sure, don't! Once you get a few users who trusted you and put their time into your project, no matter if it was free or not, you can't just walk away. Well maybe you can but I can't.
When you release something, you ask users to commit to your project. It's unfair to do that unless you're equally committed.
I'm a big fan of private betas, where you can flesh all this stuff out before asking strangers to put their time into your app. Very private betas, if need be - just you. Release early and often - to yourself. Maintain a runnable state at all times. Use your app intensively, eat your own dog food, evolve it that way. I like this kind of advice, not 37Signal's cookie cutter platitudes.