Totally depends on your site, your marketing, your niche.

There are gay sites with 15,000+ members (and I don't mean megasites with a ton of feeds... I'm talking membership sites with no feeds or extra benefits, just great original content), and there are sites with 100 members. And the interesting thing is... there are extremely mediocre sites that *still* have 3000+ members because of relentless, effective marketing.

I think that if you have a strong product and it's well presented and well marketed, you'll do fine.