I did a few more tests to try to record differences in boot times. I re-installed (well, re-imaged anyways) the Momentus XT while hooked up as an external drive. I re-installed it, and the subsequent boot times (as it “learned” what files to store on the SSD portion of the drive) looked something like this:
1st Boot: 1 min 33 sec
2nd Boot: 1 min 17 sec
3rd Boot: 29 sec
4th Boot: 33 sec
The boot times were calculated by me completely shutting down my MacBook Pro. Once I turned it on, I waited for the chime, and started the stopwatch on my iPhone. I stopped the stopwatch on the iPhone immediately after all icons were visible on the desktop, and the items in my menu bar had opened (DropBox, Rivet, Evernote).