I also have now experienced this problem. My Mac has slowed to a point of my first Dell in 1990 on phone line. Even used Clean my Mac out of desperation. It helped somewhat, at least i was able to reboot in safe mode. This sucks. It is heartening to know I'm not alone and the problem is WIDESPREAD!!!! Damn you Apple...do something. my computer is worthless. I can now eat lunch in-between sites.