#22 - March 10, 2009, 9:19 p.m.
This was an Ulduar issue. Previously, many bosses were taunt immune and taunt had a short range. With both of those changes, it was possible to ping pong bosses between multiple tanks in order to avoid anyone taking much damage. This goes beyond clever use of an ability by players (and isn't *that* clever since it has been around forever) and into an exploit that trivializes encounters. With this change, you should be able to taunt when you need to but not keep the boss confused and ineffective.
The diminishing returns do not actually work on the current PTR build despite the patch notes, but will be implemented soon.