I find that BK's original chicken sandwich and the McChicken are pretty interchangable . . . I mean, to my tastebuds anyway, they taste exactly the same, except that one is long (almost like a hoagie), and the other is round.
But, I notice other fast food joints are starting to copy Arby's now: Chick-fil-a just came out with their version of their smokehouse brisket (which is a pretty good sandwich, but danged do you have to be dying of starvation to kill off one of those things), and now Hardee's is pushing their version of the classic roast beef sandwich that Arby's is famous for. I mean, it's pretty blatant.