For iPhoto’s Faces feature, the update resolves an issue that could result in slow performance when displaying suggested matching faces, as well as a problem with some faces being matched incorrectly.
Apple offers an extra bit of advice for those who’ve imported pictures using iPhoto 8.1:
Important: If you imported photos of people while using iPhoto 8.1, there’s an extra step you should take after installing the 8.1.1 update. Select all those photos, Control-click to open the contextual menu, and then choose Detect Missing Faces. This will redetect the faces in those photos and correct any face recognition issues introduced in iPhoto 8.1. You should not quit iPhoto during the Detect Missing Faces process.
The update also resolves an issue that caused book order panel information to be displayed incorrectly in some languages, as well as fixes a problem that caused the icon for iPod touch (2nd Generation) to display incorrectly in the source list.
Apple recommends all users of iPhoto ’09 install this update—although, to be honest, I’ve yet to see a software update that Apple didn’t recommended users install. The update is available via OS X’s Software Update mechanism or by visiting Apple’s support Website.