sounds like my own story. Around two weeks of PoE without any problems, then the slow motion bug appeared. Frame rates are still very good. Other games are also affected.
Checked the forums and tried lots of things (driver updates, .net-update, graphic settings changes, heat problem checks), but couldn't find a permanent solution.
Every third or forth reboot fixes the problem temporarily - but with the next reboot, it is back.
Maybe PoE did something terrible to our computers...
AMD Six-CORE 3.30 GHz
Windows 7 Home Premium
AMD Radeon HD 6900
Direct X 11
Using PoE via Steam