The admins will definitely be more accurate, but looking at it..
The front page has 30 posters who started a topic, each of them has a unique name (as I'm looking at it now). The second page has about the same amount. The last date on the second page was 42 hours ago. That's 1.5 original posters per hour. Most websites have about 9 lurkers for every poster. So, you might be able to estimate it at about 15 original people come to the site per hour, or about 320 people a day.
That's not to say that 300 new people visit the site each day who have never visited before... But just that about 300 people visit the site each day. I suppose it could be a little high, but being a rough guess, but who knows...
The admins have previously referred to having hundreds of thousands of hits on a busy day. I have no idea whether those are unique visitors or just page-views, and since the site doesn't use cookies, I don't know if they can distinguish the two.