Starting tomorrow December 31st 2006, reading a DVD protected with CSS (as most DVD are) is illegal in France when it is done with a software allowing to circumvent the protection, such as VLC or mplayer which can both use the libdvdcss library. Today’s Journal Officiel (where laws and executive orders are published) says that you may be fined 750€ (around $985) for doing so. This includes watching any DVD that you have legally purchased.
Edit 2007-02-21: the fine is 750€, not 135€ as I wrote earlier! Thanks to the two people who pointed at this mistake in the comments.