5 Gruils of Thumb:
(1) Each game completed enables the system to more accurately rate a player. Sample size is important for the system to rate and rank most accurately.
(2) Great fluctuation from completed game to completed game means the system previously had a less accurate rating of you (due to a low sample size of completed games). Thus, the following inference: The system rates more accurately the more one plays (less fluctuation) and rates less accurately the less one plays (more fluctuation).
(3) Zibik and HHH are 2 of the best 5 1v1 ME
active members of all time. Most of the time their rank is based on their having completed over 40 games. However, they do not
consistently[i/] rank in the top 5 when they have completed over 40 games. My conclusion: If 2 of the best 5 1v1 ME active members play over 40 games and are unable to crack the top 5, I say the system does not measure ratings accurately enough.
(4) Best ever rankings for players who reached #1 are almost all based on that players rating after having completed less than 20 games. Counter examples: Chris, Zibik, HHH consistently have or had over 40 games played. Chris and Zibik didn't reach #1 or get their highest rating until their completed games were reduced and the system had to guess more about what their actual ability might be. HHH's highest rating ever is low compared to players who finish only 15-20 games. Is the system accurate if it can't properly rate the best players who play more games?
(5) The map and settings are loaded with luck. (See my comparison of 1v1 ME and 3v3 Europe No Cards at the bottom of the following thread: http://warlight.net/Forum/Thread?ThreadID=2832.) Thus, the more games you play, the more likely lady luck will catch up with you. Combine this rating/rank factor with (1) and (2) above, and you have a recipe for inflating the rating and ranking of players who play 15-20 games (system is less sure of your skill level AND you can better avoid bad luck) and creates a disincentive for players to go beyond 20-30 games completed (if they want to be a consistent and serious competitor for the top 5).
(6) Play 2-3 games at a time to avoid ladder fatigue and boredom so you can focus more. Though Piggy and Zibik are doing just fine with 5 at a time. So this rule of thumb is relative to your actual ability (some people need more time to think about picks/moves than others) and lifestyle (some have less time to play). I don't think this argument is the end all counter-argument to (3) above, since I think (1), (2) and (5) above better explain the underlying reasons for why Zibik, Chris and HHH don't rate/rank as well when they have 40+ games played compared to when they have 15-20 games played.