Interesting enough Streeteh, that was the first example I thought of. However, Valve did implement a patch to limit 'Bunny Hopping'. Which was unfortunate as it did used to add to the gameplay. It changed the element of the game and the make-up of some maps, which you weren't able to openly attack due to certain defensive layouts (Dustbowl - Thought not a league map, was a great benefit on, more maps like Well, where you could conc into the door, bunny hop in pretty much one hop, two most, around the corner. Conc into attic, pick up grenades, conc onto railings and hop to flag and out. The speed of the attack was just superb. As well as other maps which were effected. basement of 2fort another example as you'd be moving so fast, sentry guns couldn't pick you up) it added to the game play and it led to more creative styles of defensive and opened up the maps, which was a good thing.
The basis of the waffle above is that not all glitches are bad, so can't be dismissed out of hand (another example is the Halo 2 jumps as meantioned by 'Manlove' - teehee).
I guess any glitches which are picked up are easily patched by the developers which aren't lazy (The likes of Konami are definately the lazy type).