They call it "abusing game mechanics" now, but personally I find the act of discovery of this sort of thing possibly the most fun aspect of games. WoW was particularly vulnerable because of the raw complexity of mechanics introduced in a short timespan.
See: Gamesmanship vs. Sportsmanship
http://en.wikipedia.org/wiki/Gamesmanship
There was another time in WoW when a mage soloed a raid by discovering they could use spellsteal to steal invulnerability buffs off of bosses. (Hey... that's what it says on the tin, right? "Spellsteal"? ;) ) Anyway... That got patched. ;)
I remember playing Neverwinter Nights 1 and somehow I was able to squeeze 1 more weapon enchant than was supposed to be possible, onto my weapon, without cheating. My monk became pretty OP :)