Lot of issues with this by all accounts, not had them myself but...
If you have an SD bus with an SD card inserted while installing the update then it will stall at 44%
Its also removing lots of 3rd party software (you are told what it removes but this shouldn't happen) "CPU-Z, speccy, 8gadgetpack, a Cisco VPN client, SATA drivers, SpyBot, RSAT, F5 VPN, HWMonitor " have all been removed.
Also lots of default app choices are set back to MS services, sure that wasn't a mistake