Teek is right: weird mods deserve their own thread. So, re: WTF???? PO Mods on used bikes, got pics?, here's mine: (I was going to continue the thread with this, but figured it was time to branch out).
My old 1969 VW Bug, which some genius had thought would make a good street racer had a push switch in the back seat that would fire up the engine w/o the key. Kind of like the under-seat ignition (which, maybe out of nostalgia for my first car, I think is pretty awesome).
I know it's not a GS mod (my bike was pretty much unmolested, except for cutting the rear mud flap directly below the license plate), but still awesome. Any other awesome home cooked mods out there?
It is all in the Wiki, under Upgrades. IMHO all possible and impossible tweaks and ideas were done (and undone) by owners of GS. Most of that wisdom is here on this board. Search on.