Following his recent upgrade to the latest (and greatest!) version of iPhoto, Rob noticed some inconsistencies in the way Help was providing him information. Specifically, he had trouble with locating documentation on the new Faces feature when navigating through iPhoto's Help menu and launching the Help application. Rob was able to locate the documents he sought by using Leopard's Spotlight-esque Help-searching feature and querying for "Faces."
During our review of iPhoto '09 we did not come across any issues with the Help documentation. But we here at the TUAW headquarters at the Winter office in Hawaii are too stubborn to read directions. Rob's problem seems to be an old one that has occasionally plagued users through many versions of OS X. He points to another article at Macworld by Chris Breen which covers some tactics for wrangling Help back into line.
The culprit in this whodunit case turns out to be Help's cache file (in the library with the candlestick). According to Rob, "Help relies heavily on cache files to present its information to the user." For reasons unknown, upgrading an application does not necessarily cause the cache files to rebuild. In order to force the system to accomplish this, first quit iPhoto then navigate to the current user's home directory -> Library -> Caches (~/Library/Caches) and locate "com.apple.helpui." Once the cache file is located, drag it into the trash and restart iPhoto. Boom! You now have a working-as-intended iPhoto Help viewer.
While any application's help cache can become obsolete, Rob notes an increase in likelihood for Apple's own applications. Whether you're experiencing problems with an Apple app or not, deleting the cache file is very likely the solution. Have you had any issues with an application's help viewer? If so, which app was it and how did you resolve it? Let us know in the comments!