The Achilles' heel of the new upgrades, as reported last week, was that the MacBook Pro's SATA interface was limited to 1.5 Gbps in the latest models, down from 3.0 Gbps in previous models. Although this wasn't likely to be an issue unless you replaced the hard drive with a high-speed SSD, it still seemed like somewhat of a boneheaded move to downgrade the SATA interface without sufficient cause.
Today Apple has released MacBook Pro EFI Firmware Update 1.7, which makes the issue moot. The update allows the SATA interface to work at full speed once again.
If you have one of the affected models of MacBook Pro, grab this update either via Software Update, or else go here (requires OS X 10.5.7). More info on the firmware update can be found on its support page.
Thanks to reader Joachim Bean for sending this in.