The 2007 figure might be a little higher than that. I am member #56,744, and I joined in 2006.
Every once and a while the forum kicks unconfirmed / banned ... accounts if you will recall we lost about 35k member count when we updated the forum software and it removed those type of accounts which is why we ended up passing the 200k mark twice.

So you can use member number and join date as rough indicators, but not accurate member count.
But Susana, is under being conservative by estimating our current potential reach at 500k, when you consider that the average ratio of guests to members on the forum at any given time is about 3 to 1, that is a total of 4 times 350 which is 1.4 million for the forum alone. Now not all of them are active at any given time and the number of unique visits to the site is Less than that, but still some incredible growth.
I can tell you that the average user spends 7:58 minutes on the site per visit. So considering that some people will click out of the site rather fast, it means that a lot are spending a very long time here.
Some days we peak with .0014% of all page hits on the internet landing here, that might not sound like a lot, but the total number of page hits on the internet in a day is a vast number.