Dota 6.66b could be another fix release, Why? because IceFrog made some big changes in Dota 6.66 especially to the most popular hero, Lucifer - Doom Bringer. And changes always leave chance for bugs. So, IceFrog might release Dota Allstars 6.66b map to fix them.
Update: Dota Allstars 6.66b is released!
So, far no major bugs are floating around but this page will keep you updated with the newest updates regarding Dota 6.66b. If you are facing any problem or found any bug, share your experience via comments.