Shawn/Lassie is the biggest slash pairing and Shawn/Jules the biggest het pairing. Shawn/Gus is the one that pops up its head from time to time saying, "Hey, I exist!" which has the other fans going, "Aw, but you're like BROTHERS!" (because that suddenly matters for some reason). Gus is nowhere NEAR as frequent in fic (even gen fics) as he is on the show. *am bitter*