You don't expect to keep the DVD safe?
From my limited understanding and research on this topic, most "copying" solutions simply convert the information into another format... stripping the DVD of its "menuing" and other custom features before re-constituting it again (which is pretty scarey to me). Some let you automate re-authoring them to make up for the lack of a one-to-one copy feature. When it seems the "features" of copiers thumb through all of the DVD's qualities, saying whether or not they are supported... I'm concerned that they need to do this because you never know what you're going to get. DVD's are complicated beasts.
Here's a "shoot-out" from c|net
http://reviews.cnet.com/4520-3670_7-5024535-1.html
I have friends who routinely use NetFlix to rent and copy stuff they don't even watch. I hope they cut it out. I also have one friend who prides himself on keeping his DVD collection nicely kept and away from scratches and other perils. I think the latter friend is much better off.
If something happens to one of my DVDs, I'd almost rather search for a discount DVD broker online for replacing it, rather than thinking some watered down copy is going to give me the warm fuzzies.
JMHO,
~ Nexus