vobcopy is able to mirror the complete DVD including IFOs and such in
an easy manner (simply "vobcopy -m"). The resulting directory is fully
compatible with mplayer/mencoder/transcode and every other application
that uses libdvdread (or libmpdvdkit2).
Here again the Unix way of doing things (having several small
applications that are combined in order to achieve the wanted results)
is the better approach.
But if you only need the VOBs then simply go ahead and use mplayer.
(I'm not voting against mplayer here, I'm voting for vobcopy.)