I wouldn't boost anymore.

[TI Seven]

I was reading on Bungie and found this:

Q: Now that you have a per-playlist rating system and an achievement tied to earning a Lieutenant rating in a playlist, there seems to be more people EXP boosting than ever before. What is being done about this?

A: Boosting or doing anything to manipulate the way in which you earn EXP is considered a violation of the terms of use for playing Halo 3 matchmaking. As a result, we will be detecting and punishing people who are guilty of this. Our new system is nearly online and when it’s unleashed it will automatically detect and deal with this issue. In the interim, we are manually reviewing player activities and unleashing the Banhammer as appropriate. The base penalty for first time offenders will be a two week EXP ban – this means you will not be able to earn ANY exp for two weeks. You will also be under close scrutiny for any future infractions, potentially resulting in harsher punishments. If someone manages to slip through the cracks and boost their way to General before they are caught, we will dish out appropriately stricter punishments up to preventing you from playing entirely. Play the game the correct way or you will end up riding hard on the business end of the Banhammer. You have been warned.

Sorce: Bungie.net : Inside Bungie : Bungie.net Blog