I just spent way too long trying to figure out why VLC wasn’t opening DVDs. I was getting this error in the log window:
no access module matched "dvdnav"
Turns out the problem is that VLC 1.1.11 only has 32-bit versions of its DVD plugins (or perhaps its 64-bit versions are broken–the end result is the same). So if you download the main 32/64 bit universal binary from their site it will not work unless you check the “Open in 32-bit mode” checkbox in Finder’s “Get Info” window.