Should I start showing people my beta service now or wait for a bit more polish?

This is a silly question to ask a board full of agile-bodies but I am curious to get a consensus of how readers on this board feel about this question:

I have a very early beta up of a free service I'd like to offer (and maybe even open source). I feel the timing of it is right, and the service useful, but I have little time to work on it and so it could still use several weeks of hard polish and testing.

That said, I feel that given what is currently happening in the world of social services (app.net, twitter's api changes, etc), it is timely.

Do you feel it's better to take another week or two and add a bit of spit shine, or should I start getting feedback immediately?

I expect the answer most people will give is to just get it out there so I can find out if it's what people want, and if not, why. But there are definitely cases where that might be a mistake, and I would like to know what things someone might be cautious of when making this decision.

Thanks to all you great folks at HN!