I followed the link referenced by Kiran_K_Ayyalasomayajula, I read that amongst the other items, the PD10 seemed to be having problems with CPU's. My system, which was having problems, was configured to use 4 CPU's. The referenced article suggests adding a "DEBUG" parameter to the startup of your system. Instead of trying this I simply reduced my CPU's to 1. I now have a fully functional VM running with pre-yosemite speeds. This includes after reboots. Why this works is unknown to me however I am not complaining. I am running a iMAC 2011 (early model) with 32GB of ram and a mixture of SSD and hard drives. I can now display my windows start screen with zero "delay". Instead of 40-90 seconds it is immediate.
While I would prefer to use more CPU's, if one works, who am I to argue with success. Hopefully this helps someone. Again, I made no alterations beyond Yosemite (retail final release) which is running a fresh copy of PD10.1 (28600) which according to Parallels is the "latest".