Apple today addressed the issue with the release of MacBook Pro EFI Firmware Update 1.7, which allows the new MacBook Pros to utilize the full 3.0 Gbps interface.
MacBook Pro EFI Firmware Update 1.7 addresses an issue reported by a small number of customers using drives based on the SATA 3Gbps specification with the June 2009 MacBook Pro. While this update allows drives to use transfer rates greater than 1.5Gbps, Apple has not qualified or offered these drives for Mac notebooks and their use is unsupported.
Full details on the update are located in the associated support document, and instructions for installing the update are included in the update application package. The update weighs in at 3.35 MB and requires OS X 10.5.7.