Personally, I'd rather fill out a captcha each time than have an account. I just don't see a reason why I'd need an account. However, I suspect that this might be a pretty diverse issue (i.e. people feel strongly about each side, so there's really no right answer and compromise is difficult).

Why do you really need a captcha? Have you seen for sure that spambots will target you? I'd recommend (at least initially, while it still scales) that you just let people post. If spam becomes an issue, moderate. If that doesn't scale, then I'd move to a captcha system. But don't build it in unless you know you'll need it.