<< has the dcma held up in a court of law? just because it's there doesn't mean it's legal. >>
The DMCA has held up in California and New York courts (specifically MPAA v. Reimerdes in New York, I can't remember the California case at the moment,) unfortunately. Even more unfortunate is the way it has been held up, and that being the sections that redefine actions that were once considered "fair use," taking precedence over the sections that specifically mention fair use inside the DMCA itself.
Judge Kaplan's (of New York) findings are available online in pdf format (if I remember right the total is around 96 pages, makes for interesting reading if you're bored one day.)
*edit*
And as has been said before, DVDs and the new copy protected CDs (ones that don't play properly in computer cd-roms) are completely different animals than your tradition CD, tape, vhs, etc. Because they use what is legally defined as a "content control system" and when you dig around inside the DMCA (which is a law, not an agreement) you'll find that it specifically makes circumventing, or publishing tools that can circumvent content control systems illegal. The only current method to backup a DVD is to circumvent the encryption system ("ripping" it to your harddrive) and thus, backing up your DVD becomes illegal. (Same principles would apply to the new copy protected CDs, if you violate their control system in anyway, basically if you use it in any method not intended by the author, it becomes illegal.)