Yes, I duplicate my DVDs. All of them. Or at least I try to. I’m not talking about ISO images grabbed from the peer-to-peer repository du jour, but stuff I liked enough to buy. The round plastic disk distribution thingie has a very nasty side-effect: it fucks my laptop’s reader. It won’t happen immediately, but after a few dozen movies and just enough time beyond the one year warranty the unit starts mis-behaving – blocking the system, spinning like crazy, overheating etc. The main reasons for this behaviour are simple:
1. poor quality physical media
2. intentionally added errors
Both of the above have been introduced as copyright protection measures. Now my DVD reader does not cost $20 (the usual no-name PC desktop unit price) but $200, US. Since I don’t live in the US of A, a hardware failure might cost me $400 and one month for delivery. So I fear original disks. And I immediately try to convert them into .iso on a more reliable storage medium. Hints:
1. For the PC – Nero (Pro, if you have the money, not the OEM version) and Xilisoft’s suite of tools
2. For the Mac: Roxio Popcorn (very good, no trial version available unfortunately), DVD Backup (open source, I think, link to Softpedia as I don’t know the author), Apple’s own Disk Utility
3. For Linux: dd conv=noerror if=/dev/cdrom of=image.iso

Edit: just discovered MacTheRipper (dig around, you’ll find a working mirror) – so far it’s done a perfect job with all the disks which Nero couldn’t and Popcorn wouldn’t handle.