This is exactly how I felt. All 3 of my bikes have (or had) this thing, and I never gave it a thought. In fact, it was a couple of days before I noticed it was gone. I had all the spokes replaced on the rear of my old Diamondback mountain bike in the early 90s. I got it back with the dork disk, but it was something that I never thought about.

Now, I'm finding that there is all kinds of controversy and disscussion concerning this little piece of plastic (my Schwinn has a metal one). As for the bike shop; this place deals in nothing but the really high end bikes and accessories. I go there because they are very close, and they get things done quickly. I don't doubt their expertise; but I also think that they left off the dork disk because they don't like them, and either assumed that I don't either, or that I just don't know any better than to leave this thing on my bike. I'm suspecting that the latter may be the case, since the reflector was still on there too. But, I wonder why they didn't take it off?