Tom Clancy's Rainbow Six: Vegas/Boosts

Terror hunts
Completing a realistic high density terrorist hunt will give you 600 experience a game when you complete it the easiest map to complete the terror hunts on is LVU campus.

Countdown Super fast
This boost is now only worth 50 experiance every time you do it but can be done in under 30 seconds In the level on Co-Op story mode, walk towards the elevator door. Hold then let go then press. You will walk through the elevator. Run upstairs (wearing no armor for more speed makes it easier). Go towards the missile, and step to the back left side hold to disarm the missile then run like the wind. You will win without the enemy respawning.