Some players have contacted us about MMR accuracy, believing they should be higher on the leaderboard.
Firstly, make sure you have played a good amount of games. When you start out, your MMR is unknown to us, and the system has to guess at your skill. Don't spend too much time thinking about MMR if you haven't uploaded at least 100 replays, and preferably more.
If you have a lot of replays uploaded, how can you determine if the MMR I calculate is accurate? Look at the individual players' MMR in your matches, and each team's average MMR. Generally, each team's average MMR should be pretty similar.
There are times where MMR isn't accurate. In cases where established players have only uploaded a few replays, their true MMR is unknown to us, while Blizzard probably has a pretty good idea of it. If a player's change in MMR after a match is significant (a change greater than ~50), that player's skill is still somewhat unknown to us, and we have to make guesses on what their MMR actually should be.
The best way to improve the accuracy of my calculated MMR is to upload more games :) Ask your friends to upload theirs; the more replays we can look through, the more confident we can be about skill levels.
On a related note, it is encouraging to see many of the more famous pro-gamers in the top 100 of the leaderboard, as well as in matches against each other :)