In my opinion, not showing anything until it is complete is possibly the best way, for everybody, for two reasons:
It's good for the creator because gimme-pigs don't mob the creator, and he can get more done with a better chance of finishing because he isn't being bugged and irritated to the point he's ready to throw it all out the window as far as he can. (!!)
It's good for the community because it gets a pleasant surprise when the project's released, and the community doesn't get disappointed if it is not going to be released, or becomes vaporware.
However, IMHO there is wrong with showing what you can do, even if you don't plan on releasing it. I enjoy looking at others screenshots of their work, myself, even if I personally won't be able to use whatever it is that is being shown off.