I had similar problems to tarasis. Updated with the combo update and then would not boot. Hung after the apple logo and rebooted continuously. With verbose, it hung after attempting to load audio drivers. I could boot in safe mode, but video was very laggy. However, I could boot to my backup drive (10.10.3) with no problem. i tried removing all kexts but FakeSMC and there was no change. Removed the ssdt (version 1.2 of Z97-A) and all works well now. I'll have to see if there's a later version of ssdt that may help. It runs fine without it (and did before) but based the comments I've read it sounds better to have the ssdt in place. So... you may try removing the ssdt if you haven't yet. I also notice that if I 'verify' the disk in disk utility, I get the error "The partition map needs to be repaired because there’s a problem with the EFI system partition’s file system." I dare not actually try to repair that, as i presume it will erase the clover install. It didn't say that on 10.10.3 when I checked the disk.