Info on active users on November 2nd:

2007: 1010 users
2008: 2562 users
2009: 3179 users
2010: no info due to forum rollback, 3821 users on Aug 1st and 4034 on Dec 6th
2011: 3205 users
2012: 3723 users
2013: 2962 users
2014: 4629 users
2015: 4399 users

We had most users on the week following Steam release, 25k users daily average.
More people playing when it's summer, less people all other time.
Also as you can see we now have more active users than in 2009. Less than shortly after Steam release of course, but still that's more than ever before that.