A lot of people are talking about brink and its attempt to merge single and multi-player, but will it work? My main concern will be using single-player to achieve amounts of currency no-where near possible to acquire on multi-player. This could be done in a few fashions.
Grinding. Grinding is a simple way to acquire any drops or currency and its used in many video games. From pc to xbox, single-player to MMO's, grinding has been a problem from the start. Now don't get me wrong, if you want to run that mission five or six times so you can get that rare drop, be my guest. But if you only replay one mission because you know exactly where to shot, or what the AI will do, that’s just wrong. This tactic can be combined with my next one, boting.
I’m not one to talk about hacking, or boting, since I know nothing of the code that comprises an xbox game. (Though I do love my flash.) But many times on these sort of games people are able to hack single-player, but not multi-player. Most online xbox games are very good about checking for hackers and such, and personally I love single-player mods, because they almost always make the game more fun.
A simple fix to the above idea might be to require a person to be connected to the server to be able to earn currency or drops. This would allow some type of server to monitor your game-play. Another way would be a daily cap. With this set up, the development team could control how many points you earn in single-player, multi-player, or both. This would also allow for extra point weekends and such.
Comments, questions, tips welcome.