Today Saturday, the WoW Developers want to test players DPS by placing a copy of Patchwerk inside Ulduar. The classes have had a lot of tweaking, specially the Tanks and the mana regen changes. In order to test these please join the Europe PTR in the evening. Visit the PTR 3.1 Bug Forums to report anything out of the normal.

Blizzard Quote:
Daelodev: So we have a version of Patchwerk at the entrance of Ulduar to be used for DPS testing. We’ll turn it on during various times of testing. Please post links to parsed combat logs here. This will be of great help to us!—source