out of curiosity, I've created a server list scanner which regularly gets the player info from all servers on the master list and then attempts to count real players and bot numbers on all servers, eventually putting this into an MRTG graph:
The graph has to be taken with a grain of salt because of the inherit unreliability of the server query protocol and the fact that the bot detection heuristic is far from foolproof: It checks for a list of the known 2.0 gamecode bot names with any prefix or suffix and 0ms ping, with some additional hardcoded rules for servers with known modified gamecode and/or still running 1.5.
You can see the full server list including the MRTG weekly/monthly/yearly graphs (not much in there yet) on http://delight.vapor.com/serverlist.php
Sxen