I rip store bought DVD Videos to my hard drive, re-encode them, and record them to 1 dvdr backup. Quality is really the same to me. I'd say it's like comparing a 256kbps cbr mp3 to the actual CD wave file. Pretty damn close, but I guess if you're one to stare at the screen at every damn single detail, then you could possibly see a difference.

PS2 DVD games you can do 1:1 copies and play with a modchip (easiest dvd backup to do)

Xbox DVD games you can copy to the xbox hard drive, or ftp to the xbox, and then copy the dvd to your pc hard drive, then make a backup and use with a modchip.

I've done them all, everything work's great for me.