Technically, ripping DVDs to divx format is illegal if there is any sort of copyright protection present, even if you own them and only want to use them yourself, you can't even legally make a "backup", according to the
DMCRABut, noone (that I know) has been arrected, and I'd suspect that blockbuster has no right to accuse someone of this even if they do rent out 10 movies a day, refuse to provide them service sure, but unless the guy was keeping the originals and returning copies, or selling copies, then theres no way they can speculate like that without getting sued, whether he's doing it or not.
So, the discussion of such manners I would suppose is still legal, as it shouldn't voilate any of the 1st amendment restrictions, however, it is up to jeph whether he will allow the discussion of these (theoretical) activities.
One legal way to go about ripping dvds would be to take the analog signal from your dvd player playing the movie and record it digitally, because the analog movie has no protection.
As for putting it back on dvd, many players just outright support divx, however maybe NERO will have somthing to burn a movie dvd from divx.