Just out of curiosity... If you use the Split function on DVDFAB Platinum, to put the movie on two SL discs, can the movie be rejoined later to form one DL disc?
From what I've read in other threads, this option is not yet available. I believe they referred to it as re-authoring.
Not with DVDFab (yet). DVDShrink will do it.
Just to follow-up on the always solid advice from signals, here's an excellent guide on re-authoring with shrink. Navigate down to re-author and you'll find several guides, eg., "basic", "intermediate", "compilation"...
"Merge" feature will be available in near future beta version, please wait.
With "Merge", you can combine two or more discs into one disc. You cannot preserve menus, just selected titles(chapters) one by one.