ive used them and .swf's with cinemar, before i dove into jriver.
They were nice, we used them for making theater skins, icons etc. so if you knew how to make them you could have your whole interface be animated (animated background, animated icons)
example when someone would hover on the cd png i made, it would spin, and then if they clicked that spinning cd (meaning music/audio) then a small audio clip would play. A line from a local band named slave raider" Alright Alright Alright, Let's get this Record Started! while you were searching for what to play from audio section.
for movies i had a png of a theater screen, once hovered over the theater screen it would act like there was pictures moving in it, once you clicked the theater screen, then the png would bring you to all of your videos so you could chose what you wanted to play, and a small clip would play from jim morrison "is everybody in? is everybody in... the show is about to begin." lol
was neat, people got a kick out of it.
but also got a bit redundant, when going from home screen to other media types, in the same sitting.