There is a book that was transcribed from German? about the connection between a rider and the bike that I've always wanted. Also, just my opinion, but the proficient motorcycling book is worthless if you've been riding any length of time. It's very very basic. I'm looking for more stuff like the RLAP series. Advanced riding techniques, more science less anecdotes.
Not that it's a skills book, bit I liked the Iron Butt Rally book, "Against the Wind."