Oh, and it's worth mentioning--I fully expect Apple to remove the optical bay entirely in their 2012 design refresh. Mayyyybe they'll keep a second bay as a stock option, but I doubt it!
I expect they will make the whole line thinner using the SSD form factor from the Macbook Airs, but perhaps offering up to 512GB since the MBP laptops are still going to be quite large compared to an Air.
It's also feasible that they could fit a normal SATA form factor drive and the new slot-style SSDs in a thinner form factor.
They'll have to release some product that makes it easy for non-technical folks to offload low-performance files to the spinning disk versus the SSD, or they'll just market the spinning disk as a built-in Time Machine + Auto Save target.
