In comp if you play a close match it usually drops 3-5 crates. Someone told me before that you only get 2 drops per week, but one of my buddies got 4 drops in the past 3 days (can anyone confirm if there is a cap?).
This is what I heard that as one plays the drop rate increases if you haven't gotten a drop. And when you do it starts to decline until the next week, where it should reset and restart the process again.