OWC is reporting that the June 2012 MacBook Pro 15" (non-Retina) is showing solid 6G SSD performance in the optical bay, something which has been a problem with the prior models. Perhaps the new Ivy Bridge chipset is involved, or perhaps Apple has fixed some engineering bugs.
Using the OWC Data Doubler, one can install a 2nd drive into the optical bay of the MacBook Pro (by removing the optical drive). In the past, using this connector with a SATA III 6Gbps SSD has been problematic. It looks like the issue is resolved in the June 2012 Macbook Pro 15".
This test data is from OWC; I have not tested this myself. Shown below is speed with 2 X 240GB OWC 6G SSD in a RAID-0 stripe.