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.
A long time ago I wrote about scouting, and I really think it'd help you to go back and take another look.
The purpose of scouting is not omniscience. Getting that level of scouting would cost too much time and effort and just wouldn't pay off. Instead, scouting is largely to get an idea of what they're doing at the current moment.
You don't need to know every time they build a Starport, or take a new Expansion. You don't have to be on the ball with your army half way there to counter whatever crazy tech switch they're about to pull, if that were the case this game would be all about deception and hiding your next building.
Keep this in mind when you're considering the following.
The number one way people scout is skirmishes. This may seem like a strange concept as it makes sense to want to know what your opponent has before engaging them, but usually the way player figure it out is those quick little back-and-forths in the middle of the map, or the drop in the back of the base, or a fly by with a group of Mutalisks.
The reason these are so telling is they give you an idea of what he has right now, and where he's going. Notice he added on a couple Vikings since your last fly by? Maybe you see a Colossus laser eat your dropping Marines. Personally, I always find Thor missiles to be a good indicator that he has Thors... and probably more coming.
With the exception of maybe some Dark Templar rush or Hidden Void Rays there isn't a lot your opponent can build up in secret that will make a huge difference; and for those sometimes cheesy plays, there is no cheese that can't be handled by standard play. Unless you're going for some crazy Cheese yourself you should be in a good place.
So my advice to you: Stop worrying so much a live a little. Sure maybe when you suicide a Marine for intel he doesn't see a Carrier, but you know what? Unless you're doing something crazy, that's ok. You'll catch them before he has more that 2-3.
Alright Tzenes, if trick plays aren't some unmanagable thing, why am I Scouting?
Scouting is supposed to give you a feel for what your opponent has. Its supposed to give you answer like: BioMech on 3 Bases. Its not for things like: OMG he built a tech lab on his second Starport! Starcraft isn't precise enough a game yet that you can know exactly what that means and how to counter it. Maybe for the first 3-4 minutes of the game, but after that point you just need a general feel.
No Zerg player can go Muta/Infestor/Broodlord/Ultralisk in a undecided game, so chances are if he's producing one of these you probably know what to expect and where he can go next.
Best Answer
All Starcraft II players who played at least 5 ranked games are placed in a league. A league is a sort of a translation of the skill of the player. 7 leagues exist in Starcraft II: (from lowest to highest)
You can find a good league description in Liquipedia and you can find some good statistics about league repartition, by regions, on sc2ranks.