I wasn't sure you see, but if the game has a glitch then it's the developers error, if the player get's banned then so should the developers. Left for dead 1 n 2 are briming with them, no one has got banned from that.
I'd say if you're getting a big benefit from the glitch. I.E. leaderboard places etc or extra EXP or something then they may well ban you for it. For something silly like duplicating weapons in Left 4 Dead or climbing out of maps on Halo in co op play I
doub't they'd do much to you.
From what I've seen in the Support Forums, people don't tend to get banned for using cheats/exploits on single player games. They only get banned when using cheats/exploits on online games as it ruins other people's experience.