From the wikipedia article on libdvdcss:
Unlike DeCSS, libdvdcss has never been fought over in a courtroom, in part because Section 1201(f) of the Digital Millennium Copyright Act authorizes such circumvention for purposes of software interoperability.
Some operating systems (debian) believe that they are not allowed to distribute it so they don't:
http://lists.debian.org/debian-amd64/20 ... 00418.html
It all depends on how you think. It hasn't been fought in a court room -- so you can't use previous cases to base your own potential defense on. The DMCA supposedly allows it so you should be able to use it legally. On the other hand, if an OS like Debian isn't distributing a file you probably shouldn't use it. If they get sued for distributing it they will loose lots of money in court --- money they don't have. They're hesitant because they don't know for sure. If you're hesitant you shouldn't use it either.
Sorry, but I'm going to say this: IANAL -- talk to a lawyer. A lawyer will make sure 100% if you should be able to use it or not. Of course, nobody has enough money to hire one -- a competent one anyway.
Realistically, you shouldn't have any problems unless you're distributing it in large quantities (by the millions) -- "De minimis non curat praetor - The ... law does not care about trivial things."
http://en.wikipedia.org/wiki/De_minimis
Who knows what's trivial, though? The RIAA just won a $222, 000 lawsuit against a man who shared only a few songs (24):
http://arstechnica.com/news.ars/post/20 ... is-in.html