I tried Instant Copy the other day and I wasn't impressed with the quality of the movie, because it doesn't spend much time on reencoding it. I can only assume that it just does one CBR (Constant Bit Rate) pass, so that it is fast. I was impressed with the idea of being able to keep all of the menus and stuff, but it doesn't let you take big extras out; only reduce their reencode quality. I think this program has a lot of potential though. They just need to give you more options.
If I want to make a backup of a DVD, I use CCE and do a 5 pass VBR (Variable Bit Rate) to keep as much quality as possible while reducing the size of the movie. This only takes a few hours to do on my computer (Pentium 4 overclocked to 4.2GHz). After that I just compile it in DVD Maestro with the audio tracks I want (like 6 channel AC3 and DTS). Of course, I don't get to keep all of the menus and extra features, but I don't really care about that stuff. I know that you can use IFO Edit to keep the menus while reencoding the movie with almost any program--I just don't think it's worth it.
I have also used DVD X Copy. I like that it allows you to keep everything with its original quality, but I don't like that crap it adds before the beginning of the movie. It also gets rid of everything that originally played before the movie would come on (still on the disc, but doesn't show it) and it does some bizarre things to some of the more sophisticated DVD's.