These firmware updates aren't the sexiest announcements, but if you're running a mid 2010 iMac with hard drive issues then it should come as welcome news. Apple's latest patch fixes a hard drive issue that may prevent iMacs (of the 21.5-inch and 27-inch varieties) from booting properly.
The 767KB update, which requires Mac OS X 10.6.7, is available through your computer's Software Update or through the link below.