"According to Johansson (a former program manager for security policy at Microsoft), there appears to be two separate issues. One affects only AMD-equipped PCs sold by Hewlett-Packard Co. "The problem is that HP, apparently along with other OEMs, deploys the same image to Intel-based computers that they do to AMD-based computers," said Johansson. "Because the image for both Intel and AMD is the same, all have the intelppm.sys driver installed and running. That driver provides power management on Intel-based computers. On an AMD-based computer, amdk8.sys provides the same functionality." Running the intelppm.sys driver on an AMD-powered PC isn't normally an issue, but on the first reboot after a service pack installation, it causes "a big problem," Johansson said. The machine either fails to boot or crashes and immediately reboots.
The other problem, according to Johansson, also seems to affect only AMD machines, and involves an error message indicating trouble with the PC's BIOS. Johansson said that the ensuing recommendation to update the BIOS is "most likely not your problem," but said that the problem may be isolated to a specific motherboard. "Possibly, it is related to computers with the Asus A8N32-SLI Deluxe motherboard in them," he said.
Johansson also spelled out workarounds for both problems on his blog. The HP issue can be solved by disabling the intelppm.sys driver, while the second fix requires the user to plug in a USB flash drive before booting."
Doesn't really sound like a Microsoft mistake, they may share some blame though. I've installed the leaked and the official SP3 on many computers (notebooks; retail and homebuilt desktops) without a hitch.
Thanks go to the OP for the heads up in case I run into such a problem in the future.