If you have been worried by the reports saying that the Macbook Pro 2009 hard disk performance was capped to 1.5Gbps, we have some good news for you: a fix has been issued!
Just as we thought, this was a software issue and a fix in the EFI Firmware 1.7 is said to patch the problem and restore the SATA speed to its full 3.0Gbps theoretical speed. You can download the update at this Macbook Pro support page, but Apple warns that this is not a supported update.
Previous rumors suggesting that Apple had cut down on performance to cut prices were indeed totally bogus. The hardware does support full SATA II speeds. Update 6/25: I see the firmware 1.7 in the Mac OS updates now, problem solved.