I don't think I have ever paid full retail for a new bike -- at a minimum, I have gotten accessories, helmet etc tossed in with the deal.
I think a great deal depends on the bike though. I wouldn't count on getting much of a discount on any Harley (they have been in such short supply for so long that the dealers don't remember concepts like bargaining) or on the new Honda 600RR, because there will only be a few available until late summer.
I have gotten a couple of great deals on leftover models -- I once bought a brand-new, but 1-1/2 year old, Yamaha 650 Seca for exactly 1/2 of suggested retail price, 2-days before the dealer filed for bankuptcy. I bought my 1995 Ducati in the summer of 1996 for $7,000 out the door becasue the new owner of the dealership needed to clear the inventory of old bikes to make room for the new (he also had incentives from Ducati North America). Of course, given how much I have since spent at that dealer for tires, pipes, tuneups, dyno work etc, he could have given me the damn thing and still made a profit!
Maybe someone here with past motorcycle sales experience can give some guidelines as to what markup the dealers have to work with.