In an effort to create a better game for their Mass Effect audience, BioWare has been secretly loading up up on stats of how people play Mass Effect 2, and the second batch has been revealed. Using "events," which are pretty much what the player does and their choices, the ME2 developer found some pretty useful information. From what's been revealed via Destructoid;

• 83% of players created their own face for Shepard
• 82% play as male Shepard, 18% as female Shepard
• The Soldier class is far and away the most popular class at 65%
• <Archangel> was among the most popular squad members selected for missions
• 10% of players never let <The Krogan>
• Only 50% of players have fully upgraded the <Ship> by the end of the game
• 14% of squad members die in the end-game, on average
• 36% of players chose the <Renegade choice> in the end-game

From what Casey Hudson told IGN a few months ago, how this whole "event" thing works is like this,

"The only data that we get are in terms of events -- little things that happen in the game...Let's say if we want to know whether players skip lines of dialogue, we can have that become a little event that gets sent up. It's all completely anonymous, so all we get is raw numbers for how many times these kinds of events occur. Then we can start getting ratios and comparing proportions and things like that. It becomes this mass of numbers, and then we have to try to figure out how we would interpret that."