OK, most retail DVD's are dual-layer which = DVD 9
Some however are single layer which = DVD 5
The DVD-R/DVD+R you burn on your DVDRW drive are ALL single layer 4.7 GB = DVD 5
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So in reality a DVD 5 DVD can be backed up almost as easily as the average music CD, you still have to rip it to your HD first to remove the macrovision/region prot, etc first though. Then you can easily burn the image back to DVDR.
With the bigger dual-layer DVD 9 DVD's things are of course not so easy, the new kids on the block (Such as DVD20ne & Instant Copy 7) get around a lot of steps by using a clever process of transcoding which makes it much easier & quicker to copy a DVD than using the old tried & trusted methods. In the case of DVD2one for instance it only seems to take aprox 20 minutes to do this after ripping which truly is amazing.
Hope this explains it clearly.