I only have one bank of registrations, and I mostly use them to change right-hand sounds.
I have around 30 "Favorites" in the Music Finder. They are more "genre" setups that songs, really. They cover most of the songs I do. It's easy enough to change the tempo if necessary before starting a song. The basic sounds I use on 90% of gigs is accoustic guitar, electric guitar, pedal steel, piano, sax, organ, fiddle and strings. I do use the OTS on many soungs, in addition to my 8 favorite sounds set up on the registrations. (Actually as many as 16, because I have Main and Layer set to different sounds in many cases.)
Like Dave, I may use more Registration eventually, but I find that making myself learn to call up settings on the fly allows me to explore the keyboard and quickly learn to navigate it.
DoM