Obiter:
Glitches can be a good source of innocent fun too.

The early days of WoW (and before there were PvP Arenas or Battlegrounds where this could be exploited) had all kinds of terrain glitches that made exploring the nooks and crannies occasionally quite surprising. It was addictive in some ways. I always enjoyed spotting an interesting off-limits set piece area during a fly-over and seeing if I could find a way to get there.

I have to believe that Blizzard left a few of these in as "easter eggs" for the adventurous to find. The airfield behind Ironforge, for example, had all kinds of planes and buildings and scripted fights even during the beta testing period. That strikes me as a fair bit of hand-made content to leave in the game when people wouldn't (in theory) ever be able to see it up close. There was even a little sign at the top of the mountain nearby.

Other glitches can actually expand the gameplay or life of a game. MarioKart 64 for example had a famous glitch in the Wario track where you could skip large portions of it -- but which also took some solid skill and timing to pull off. Some of the best and most intense races I had against other people was where we'd both be using the exploit and knew that one screw-up would loose the race.

Agreed. Who here remembers the old Pokemon clone glitch? It can only be used in Pokemon Crystal and earlier. First, you save. Then, you withdraw a pokemon you want to clone. Then, go back in and switch boxes. When you save, turn off the power as it says "Saving...do not turn off the power." When you return, you should have the pokemon with you, and in your storage box. I think that's the process.