As Mugahay says, it all depends on what it's used for.
My only glitch example I can think of at the moment, would be Call Of Duty 2. The Xbox 360 version was patched up after it was discovered a whole stack of glitches within the Online stages. People were able to hide in the background, and shoot people down without being spotted. This would be a classic case of cheating, I suppose.
When glitching isn't cheating, umm, Call Of Duty 2 again, one of the stages had a glitch where you could camp in a tree. This spot isn't really cheating, because you still could still be seen in the tree. I'm pretty sure that was the only glitch that wasn't patched up. Again, I'm talking about the Xbox 360 version here...lol.
02/04/2008
Mario and Sonic at the Olympic Games
Gold Coast, Queensland, Australia