Another easier way to back up to DL disks is to use DVD Decrypter (free program) to rip the DVD as an Iso to your hard drive and to burn back the Iso to a DL using DVD Decrypter.
If the movie is slightly bigger than to fit on a DL disk then yes CloneDVD will recode it slightly to fit and you will lose very little quality. Theres a percentage bar in the program to tell you how much quality is reduced. If this bar is in and around the 50% mark then you will lose alot of quality. If the movie goes over say a few hundered megabytes then it will probably be in the late 80% to early 90% which would result in very good quality.
Currently, DVD+R disks which have been bitsetted to a DVD-ROM disk give the highest compatability. If you have a relatively new DVD player then chances are that it will play all kinds of disks i.e +R -R. Some older DVD players had problems playing +R disks. A DVD-ROM disk in theory should be able to be played on all dvd players.
There are no -R DL writers on the market yet. One of the best DL Writer on the market at the moment is the NEC 3500 which can write +R DL disks