I disagree... users love seeing new features. If they don't work so well, they don't care. Most likely they'll enjoy them and feel privileged they are getting to use them before they are really ready. They'll see the potential. They'll start imagining what it'll be like once it's finished. If it's a cool, innovative feature they haven't seen before, they'll see it as proof you're a cool place to be. Even if half of it doesn't work.

Get features out often. Of course make sure they don't break anything else, or reduce the users experience, but users love to see a site evolving and changing with them on board.