To determine if your issues is due to the same problem wither SSH into the computer once booted if remote login was enabled or boot to Recovery Mode and launch the Terminal. Then run the following to see recently logged errors.
tail /var/log/system.log | grep 'Segmentation fault'
Or if using the Recovery Mode terminal the following thought the drive name may be different.
tail /Volumes/Macintosh\ HD/var/log/system.log | grep 'Segmentation fault'
If either of these commands produce any results that you have found your problem. The culprit is Unsigned Kernel Extensions or .kext modules. In the good old days developers could just install these as needed to add code level kernel functionality but no for improved security OS X requires that all Kernel Extensions be signed by the developer. This is overall a good thing because these are privileged and could easily lead to malicious behavior by untrusted sources.
Anyway the problem where is that the upgrade didn't disable the unsigned Kernel Extensions it found and instead just doest't load them. This is fine and normally it would just mean that whatever applications depend on them would jus not work until updated but for whatever reason there are a few special cases that cause the login process to hang. I ended up removing all the Virtual Box and Soundflower modules and then was able to boot without issue. I have not tried to Re-install or upgrade wither yet but atlas my computer boots.
To remove these again go to the Terminal and do the following. You will nee to authorize them with your administrative password.
sudo rm -Rf /System/Library/Extensions/Waco* sudo rm -Rf /Library/Extensions/VBox* sudo rm -Rf /Library/Application\ Support/VirtualBox/* sudo rm -Rf /System/Library/Extensions/Soundflower* sudo rm -Rf /var/folders/*
Again note the additional prefix if using the Recovery Mode ant that thedick name may be different.
sudo rm -Rf /Volumes/Macintosh\ HD/System/Library/Extensions/Waco* sudo rm -Rf /Volumes/Macintosh\ HD/Library/Extensions/VBox* sudo rm -Rf /Volumes/Macintosh\ HD/Library/Application\ Support/VirtualBox/* sudo rm -Rf /Volumes/Macintosh\ HD/System/Library/Extensions/Soundflower* sudo rm -Rf /Volumes/Macintosh\ HD/var/folders/*
Finally just reboot and enjoy.