Our DM used one in the form of a Chaos Portal owned by a Slaadi crimelord who used it for laughs. In our instance, if we wanted a time extension to a job he'd requested us to do we had to walk thru the portal.........all of us!
Mage walks thru - Lose 10k xp.
Ranger walks thru - Gain 10k xp.
Sorcerer walks thru - Lose all wealth.
Cleric walks thru - Lose all wealth.
Samurai walks thru - Gain +2 to a stat of your choice.
Paladin, (me), walks thru - Nothing happens..........until I slay a devil single handedly - Gain a level.
As you can see, it was a mixed bag. The mage, sorcerer and cleric took it surprisingly well. Even though the sorcerer and cleric lost some very heavy equipment, (they were both 15/16th), I think they felt it less than say the rest of us would have considering they still had considerable resources at their disposal in the form of their spells! Still it was a blow to lose all that equipment for sure and we are still in the process or re-equipping them!!!
Funny thing was is that I both me and the mage asked for another go however he would only let the mage go again but he eventually turned the second shot down. Even then he wouldn't let me take the second shot!!!

This probably has something to do with the fact that I love random stuff and it usually pays off well for me........
In a campaign long ago he got me to create a character and said you start of at X level but can roll a D100 to determine the % of XP you have towards attaining next level........one 100 roll later and I'm auto the next level!
My first character in our present campaign, the wild mage, virtually every time my spell surged it would either be maximized, empowered or allowed no save. He soon killed that one off!!!
