Apple Slipstreaming Dual 6GB SATA III Ports into 13/15/17" MacBook Pro — But Don’t Assume it Functions
One 6 Gbps SATA III port in the standard drive bay + another in the optical bay.
My replacement 17" MacBook Pro, built in early May, has a 6G port + 3G optical bay port, so apparently Apple is silently revving the build of the MacBook Pro, as I have received reports from a variety of readers that the 2nd SATA port (optical bay) in the 2011 MacBook Pro is a 6 Gbps SATA III port on the latest builds of all sizes of the MacBook Pro.
That’s the good news for new buyers. That BAD news, is that I have reliable information that on the 17" model at least, the port in the optical bay is non-functional for a 6G SSD, and highly erratic in the standard drive bay— just as with my original problem unit.
Apparently Apple has not worked out the bugs with the MacBook Pro, at least not for the 17" model. Caveat emptor.

(Apple System Profiler)