My best game ever was 32 - 2 on the Rust map. I had my kill streaks set to airdrop, turret, and harrier strike. I got 3 kills, my airdrop was a heavy gunship. I called that in, picked some people off, set up my turret in a corner...let that get me to 7 for the harrier, then I called that in. I was racking up kills so quickly because I had the turret, heavy gunship and harrier on the map at the same time. I just hung out in a corner and picked off everyone as they were running for cover. It was SOOO much fun!
The best thing about MW2 over MW1 is that you get to choose the killstreak rewards. If you pick properly, you can dominate a map! The AH-64 Apache is unbelievably fun and overkill! I've gotten 14 kills in a row with that alone and I'm sure other people have gotten more.
I've always been decent - good at shooters. I'm usually in the top 3 of team deathmatches or free for all. I just try to keep my average to 2.5 kills : 1 death. Doesn't always work out though when I get stuck in a game with other good players. As long as I'm not less than 1.5:1, it's an okay game.