On my wife’s laptop, (openSUSE 11.1 and KDE 3) it used to pop up with an option to play a DVD with Kaffeine, Mplayer, etc. when she put in a DVD. She gets other various autorun pop-ups for other things, such as when you insert a blank CD/DVD or USB drive. Kaffeine and Mplayer are still installed. I’m not sure why nothing comes up offering to play DVDs anymore.
DVD playback itself does work if she manually loads up Kaffeine.