Bill, Your situational approach sound pretty good but I'll bet it starts as many arguments as it settles. As for Blue Suede Shoes, I don't really think it's folk but I still contende that rockabilly is a folk genre (when played by country boys in 1954 :)

Chet, Your observation about blues being classified as folk or country reminds me of a record store I used to frequent in the 60's. Blues was considered folk so anything even remotely related to blues ended up in the folk bin. When "folk-rock" came along, anybody remotely related to that ended up in the folk bin unless they had a top forty hit. Cream, Hendrix, Zappa, The Fugs, Jefferson Airplane, Grateful Dead, were all considered folk.