It certainly isn't practical to store DVD movies on your computer's hard disk. I have roughly 100 purchased videos and DVD's. If I had some reason to move these movies to my computer, they would take 600G or so of disk space. With a single IDE hard disk's capacity topping out at 32G, I don't see such monstrous storage capacity coming to a home computer near you any time soon. Another stated concern is that people will start transmitting movies in real-time over the internet.
Professional pirates are a completely different story.
One analogy I heard is that it is sort of like the difference between having a really good photocopier and having a secret decoder ring. CSS is the secret decoder ring, if you have it you can use it to copy the secrets from a DVD disk. So the only practical use for DeCSS is to copy single DVD titles to your hard disk for playback. Despite legal considerations, DVD player development on Linux is continuing rapidly. You can follow the ongoing development and discussion via the Livid-Dev mailing list which will deliver an interesting digest of DVD information to your mailbox each day.