So just to get this clear; I just ordered a 2012 15" MBP and am going to also pick up an SSD. The consensus is that I can and should put the SSD in my optical bay because it supports SATA III? This SSD is going to be my main drive where the system will boot from, and I will use my stock 5400rpm drive to store media files which will be in the original HDD location. Is this correct? I have gotten some mixed advice.
That's the setup I have w/ my 13" 2012 MBP and it's working out great. I'm able to boot from the SSD w/ no problems. Temperature has not been a problem, and the HDD is not only running cool in the original bay, but it's able to take advantage of Sudden Motion Sensor feature.
The only drawback is that I haven't figured out how to get my Boot Camp installation on the SSD. I tried to make a Boot Camp partition on the SSD before creating the Fusion Drive, and it made the partition, but Windows 7 wouldn't install on that partition. It said something about not installing because it wasn't able to boot from it due to something in the BIOS. So I just combined the whole thing into a Fusion Drive and made a Boot Camp partition from that. It works fine, but it has put the Boot Camp partition on the hard drive, so performance is slow.