Should we have a section listing games that Special K breaks and potential fixes? Off the top of my head, I know of three games that are broken by Special K, and half-functional fixes for two of them.
Bayonetta - Achievements can't be collected. Fixed by setting FetchFriendStats=false globally.
Zombie Night Terror - Achievements can't be collected. Partially fixed by setting SteamPipeDLL to the file included with the game or installing Special K locally, though this seems to introduce some instability.
Resident Evil / Biohazard HD Remaster - Achievements can't be collected. I don't know of a fix for this yet.