I belong to virtualtourist.com - have done so since December 2004!
Prior to the big London 2006 meet I had only arranged one other meeting - 18 people came to that. So I thought that the Jan one would be those kinda numbers too... but 115 people signed up! I was gob smacked, and actually had to change venue three times as numbers rose as time drew nearer. I ended up having to hire out an entire restaurant in Central London (NOT an easy feat I assure you!) only when I gave them a HUGE £ deposit. 88.5 people came in the end.
Most people I have to say did cancel with me properly, only about 15 just didn't pitch on the main event on the Saturday night, which I thought was rather good. We had a wonderful time over those 3 days but NEVER AGAIN. I have arranged other things before (used to be in the wedding industry), and I actually do enjoy organising things, but arranging a meeting with people literally coming from all over the world was very stressful, replying to VT emails every day, catering for different food tastes, trying to please everyone (impossible), thinking of restaurants every day that weren't expensive (in London!???) - plus catered for a variety of tastes, giving hotel advice, travel advice, and the huge expense for one person on their own (putting £1000 in deposits down etc.). I would do it again if I were in a team of 2 or 3, but never again on my own.
Big meets are lovely if over a few days too... where people have the option to join in arranged excursions or do their own thing for a morning etc. Big meets can be a lot of fun (even if a blur at the end of it!).
Since then I have not advertised ONE meeting I have held haha. You live and learn!