As I stated in
this post, there were approximately 75,000 individual master server connections in January and February of this year, or 1,250 per day. The only thing I 'messed up' was to use different time periods for "Number of players blacklisted" and "Number of players", so the last chart shows more cheats per 1000 players than it should.
The answer to your question, MerCyKiL, really depends on what you mean by 'play AC'. Not all master server connections are somebody playing, and even if they do play, they may not play for very long at all before uninstalling the game, so this figure is highly misleading. If I
had to pluck a very approximate figure, almost randomly, from the stats and watching the servers/community, I'd guess at about 2-300 regular players (once a day) and maybe 2-3,000 who play less often, but would probably consider themselves AC players. These stats come with no guarantee of accuracy whatsoever.