Unresponsive Keyboard and Trackpad after sleep
As for me, I, too, faced the same problem with my MacBookPro after upgrading to Yosemite: the keyboard and trackpad would freeze, especially after waking up from sleep. At first, I'd restart the device. 
A few days ago, out of sheer frustration, as I clicked on random keys and rubbed the trackpad, the keyboard and simultaneously, the trackpad, became responsive, quite to my surprise. After several more tries, it now seems to me the key 'Q' was the key- pressing it several times, along with the 'esc'. I don't know how, but this works on my MBPro.
Of course I'm no techie, and have no explanation, but would request interested and affected users to try my approach.