Modders: Not cool if someone mods to give them unlimited health, etc. Though sometimes it is pretty funny to see someone with an L86 with a 1000000 RPM r.o.f. or whatever.
Boosters: Not cool at all. If you have to team up with a pal with Tactical Insertions to get headshot titles, that speaks worlds about your talent. Plus, it results in players getting flamed and harassed for using a gun wih Fall camo, even if they earned it legitimately. Thus, boosters poison everyone. THEY NEED TO BE ERADICATED. At least in Black Ops - thank you, Treyarch, thank you, thank you, thank you - boosters will be in for a nasty surprise.
Hackers: Ditto boosters - asshole c**ts who ruin the game. They claim they can't be caught, but:
Hacker: (Upon being accused of hacking) What?! I NEVER HACKED, U FAGOT!
Not a hacker: So how come your stats go off the screen, then?
So, that's my opinion on modders, boosters and hackers. What's yours?