To rip a title:
mencoder dvd://3 -oac copy -ovc lavc -lavcopts vcodec=mpeg4:mbd=1:vbitrate=1800:v4mv:autoaspect
-vobsubout title3 -sid 1 -aid 129 -o title3.avi
This rips title 3, uses no sound compression, but lavc compression for video, with a bunch of nice options (I must have taken these from the man page). The “vobsubout” selects the subtitle file name. “-sid” selects the subtitle channel (there can be many: different languages, comments…), and “-aid” the audio channel (likewise); defaults for the later are 0 and 128, I think.
mencoder dvd://1 -oac copy -ovc copy -vobsubout title1 -sid 1 -o /dev/null
This rips just the subtitles, throwing away video and sound.
mplayer -aspect 16:9 title1.avi -vobsub comments/title1
This plays the title, with a subtitle file different from the default one (which must be in the same directory and have the same name). Nice for comment subtitles.