I use DVDXCopy to split movies on two discs because I'm lazy and it's the easiest way.
After all it becomes an exact copy, I don't like to have to fiddle with settings if it's already perfect
Edit: You need any version besides DVDXCopy Xpress to split the DVD.
Be aware that because of a lawsuit against them DVDXCopy will have to take it's descrambling part out of it's software soon (within a week). So then you would have to run AnyDVD in the background.
Future versions of CloneDVD are supposed to have a movie split option, in fact I've heard that there is one already. I haven't looked into it yet though.