Yosemite stuck on boot screen - Possible M4 SSD issue

Question

I had OS X Mavericks prior to installing OS X 10.10 Yosemite. I downloaded Yosemite through the App Store on to a mid-2012 Macbook Pro 13 in.
  Model Name:    MacBook Pro
  Model Identifier:    MacBookPro9,2
  Processor Name:    Intel Core i5
  Processor Speed:    2.5 GHz
  Number of Processors:    1
  Total Number of Cores:    2
  L2 Cache (per Core):    256 KB
  L3 Cache:    3 MB
  Memory:    Crucial 16 GB 1333 MHz DDR3
  Boot ROM Version:    MBP91.00D3.B09
  SMC Version (system):    2.2f44
  Sudden Motion Sensor:
  State:    Enabled
The download was fairly quick as I upgraded as soon as the update came out. It took about 30 minutes and then locked up before the next 7 minutes to finish the installation. I have FileVault turned on and would enter the password to login to the drive and my user account. The progress bar would get to 50% and then stop. I waited about 30 minutes the first time and 45 minutes the next. After multiple reboots, the same issue would happen.
I rebooted into OSX recovery system (Option-R during bootup) and was going to reinstall OSX Yosemite. After unlocking the boot drive, entering in my Apple account info, it said it was going to take a few hours to redownload and install. I stopped it 5 minutes into the download and rebooted the Mac using the OSX recovery system exit > reboot method. Luck would have it, I was able to login and complete the install. I updated all the applications to the latest version (outside of the App Store), such as Adobe, Silverlight, etc.., missed this step prior to installed Yosemite. Everything was working fine.
During normal work, I had a lot of applications open from VMware Fusion, Office for Mac, Firefox, and then when I opened Preview, the Mac crashed with the grey screen of death. When I rebooted by holding down the power button for 10 seconds, it would only let me unlock the drive and was stuck loading up to 50% without ever getting past the progress screen for 30 minutes. I went back to OSX Recovery System and performed the reinstall OSX Yosemite and backed out again as I did before thinking it would let me log in. After rebooting it failed to get past 50%. The next reboot I was able to login.
I started thinking about the 256GB M4 SSD Firmware and noticed on the http://www.crucial.com/usa/en/support-ssd-firmware it stated upgrading from 040H (what I was on) to 070H would fix the following issues. Granted it stated for Windows and not Mac, after updating the firmware, I have been shutting down and rebooting without issue (crossing fingers).
The following is a summary of changes between 040H and 070H, which are independent of operating system:
Resolved a power-up timing issue that could result in a drive hang, resulting in an inability to communicate with the host computer. The hang condition would typically occur during power-up or resume from Sleep or Hibernate. Most often, a new power cycle will clear the condition and allow normal operations to continue. The failure mode has only been observed in factory test. The failure mode is believed to have been contained to the factory. This fix is being implemented for all new builds, for all form factors, as a precautionary measure. The fix may be implemented in the field, as desired, to prevent occurrence of this boot-time failure. To date, no known field returns have been shown to be related to this issue. A failure of this type would typically be recoverable by a system reset.
I upgraded the current Mac to a Crucial M4 256GB SSD and moved the stock 750GB hard drive to the cd-rom bay. I was able to install the update to 070H using an bootable USB stick and the method from http://forum.crucial.com/t5/Crucial-SSDs/Updating-firmware-on-Macs-without-a-sup erdrive/td-p/61259. I did have to disconnect the second drive (just lifted the connector to the motherboard) as it would not allow the Firmware update to start with the drive connected.
Seeing if this helps anyone else out with Yosemite locking up during a boot. I did not enable TRIM as I read it can hurt the M4 SSD since it has a garbage collection.
M4-CT256M4SSD2:
  Capacity:    256.06 GB (256,060,514,304 bytes)
  Model:    M4-CT256M4SSD2                         
  Revision:    070H
  Native Command Queuing:    Yes
  Queue Depth:    32
  Removable Media:    No
  Detachable Drive:    No
  BSD Name:    disk0
  Medium Type:    Solid State
  TRIM Support:    No
  Partition Map Type:    GPT (GUID Partition Table)
  S.M.A.R.T. status:    Verified

Answer 1

I rebooted my machine and was back to either getting stuck at 50% or just seeing a black screen. Both times I was using a Kensignton USB 3.0 Multi-Display Adapter as well as the Mini DisplayPort to DVI port. Once I power off (hold 10 second power button), unplug all external monitors, I'm able to boot into the OS.
Currently running DisplayLink USB Graphics Software for Mac OS X version 2.3 Beta
http://www.displaylink.com/support/mac_downloads.php