favorite mod, hands down, fabricating dual projectors for my 2006 r6.
worst mod-wasting my money on fender eliminator. bought it from gravesport cost me over $50 and its just a stupid piece of aluminum. you can make your own license bracket for $10 - $20 from supplies at home depot.
Worst mod... P O S Vortex Exhaust Hanger that I traded my Passenger Foot Pegs for. I TOTALLY got ripped off. (but that is soon to be fixed, I ordered a YEC hanger, and it truely is a unique peice in the states)