The three races are actually quite balanced compared to other RTS games.
However, I think that statistics wouldn't be a very good source of information for something like this because of the way leagues are set up. Your placement is based on who you win and lose against. However, Blizzard tries to keep your win ratio at 50% so they match you accordingly against easier or more difficult opponents to try to normalize that ratio. So if there was an overpowered race, the usage statistics and win ratios would remain relatively constant. It would probably only be visible at the very top level of play, but the game was just released a few weeks ago so it's too early to be making conclusions.
As for race usage, Protoss and Terran are effectively tied, but Zerg has less players than the other two races. See http://sc2ranks.com/stats/all/1/all. I suspect the reason for the Zerg underuse is because the Zerg macro mechanics are less intuitive than that of Terran, which players are already familiar with from the single player campaign. Some also say the race is the most difficult to learn and master.
From a non-statistical standpoint, I would say there are some tweaks needed, but overall the game is fairly balanced. For example, Terran's EMP (from ghosts) is a little bit too strong against Protoss because it drains all energy AND removes 100 shield points, yet requires no research to obtain. But you can be fairly certain that a good level of balance will be obtained a few patches down the line.