How is the match bonus in Modern Warfare 2 determined?

By far the largest contributing factor is whether or not your team wins or loses. I actually did a multivariate regression of almost a dozen factors about the game and two other largest contributing factors were your K/D ratio and your Team's Total Score (out of 10,000, 7,500, 200, what have you, depending on game type). Of course, your team winning and your team's total score may be auto-correlated (meaning that there is a correlation betweent the variables of Team Winning and Team Total Score). This means you could either remove Team Winning or Team Total Score and still have a valid model (depending on the degree of Auto-Correlation), but it would not have the same predictive power.

Bottom Line
Main Factors:
- Your K/D
- Your Team's Score
- Your Team Wins Status

Other Notes
- Total matches regressed: 34
- Data does not appear to be heteroskedastic or homoskedastic
- Correlation between Team Win and Team Total Score was 0.82
- In the data set no draws occured