Achievements
One of the additions for RC2 were Achievements. There are several types of achievements, although most of them are related to killing.
Check the images for examples of non killing and killing achievements.
There is no comprehensive list for Achievements, but you can look at the achievements thread in the main forums. [1]
Saving
The achievements are saved client-side in the file achievements.dat in the MBII folder, meaning it doesn't matter which server do you play. If you want to reset the achievements, just delete the file and it will create a new one next time you play.
Using the example of the Jedi/Sith achievement, you don't have to kill 200 people in 1 session. The number of kills are saved in the file, so there isn't a problem if you only killed 50 in a single session
Cvars
There are 2 cvars:
cg_achievements
0 - Disabled
1 - Images only
2+ - Images and Sound
cg_achievementsScreenshot
0 - Disabled
1+ - Takes a screenshot when you reach an achievement
You can also use the Game Options menu