Oh, there were a lot of interesting bugs... for example you could make someones' account frozen (like in case of payments fraud) by forcing on a player a specific sequence of movements. Player tempted with crystal coins lying on the floor made "correct" move, when he wanted to come closer and suddenly dissapeared! Just puffed, for a few days.
Another example which I remember (it took place on Guardia about 2 3-4 years ago) was throwing a huge ammount of items into the depot and setting up the bot that would get in and out of the depot SQM. It caused crashes of the whole server.