Valve has released some fun and interesting statistics on TF2. Stats include things such as most class time played, most damage from a weapon, time played on per map, etc. They also give "Death maps"; these maps contain mappings of where the least to most deaths occur.

On another tab is 'achievements' which give in percentage how many users have obtained it. The top obtained achievement is Hard to Kill (Get five kills in a row without dying.) @ 62.4% and the hardest achievement being With Friends Like these... (Play on a team of 8 made up of only players from your friends list.) @ 2.1%

It's unclear which platform these stats are for, or, if these stats are a combination of all paltforms.