After installing Yosemite my mac mini late 2012 freezes up when waking from sleep. I can move the cursor around but I can't click on anything or use any keyboard shortcuts!
I have a similar issue with my MBP retina 15" mid 2012. Whenever my MBP goes into deep sleep and I wake it up (e.g. open up my MacBook again) it shoes some weird gray screen which looks like a graphical bug. After like 2 seconds the usual login screen appears without any problems.
Another issue is that if I open an application after a deep sleep, which requires the Nvidia GPU and not the integrated one, the MBP freezes like you describe it. The cursor keeps moving, but I can't use any shortcuts or click on anything. Only way to get out of that is to press the power button and force a restart.
After the boot appears a warning,which says something like:
"A graphical bug has appeared, do you want to report that issue?"
That bug doesn't seem to appear after every deep sleep though, so I can't reproduce this error on purpose. Anybody else has this issue and is there a way to fix this? As I haven't seen many people complain about that, it seems to be a very specific error. I still sent the bug report to apple