I was unable to drop them on the dock, which was the advice of the Apple tech note.
However, I went back and also tried to drag and drop the photo from e-mail onto the photos folder in iPhoto. That doesn't work either.
My workaround ended up being to save the photo into the download folder and then drag and drop that into iPhoto. (Pretty "yesterday" solution.)
It's irksome that the software features don't work like they are supposed to and then that the tech support note is not useful.
I seem to be in good company with the problem.
Running Mac OSX version 10.8.2 on 2.53 GHz Intel Core 2 Duo MacBook Pro
Running version 9.4.2 of iPhoto.
Working fine here on all my Macs. Can't be a common, flawed feature, as it is rarely reported. Something to Troubleshoot in the iPhoto Forums.
The feature does work, but not for you, so you have something that needs fixing.