I have bought (used D&D) stuff from Amazon before, but only because I was impatient.
I think it's pretty spotty. I mean, when I go looking for an item, I don't even search Yahoo auctions anymore.
I have searched Froogle but that mostly turns up new
3E crap. (and
3E is crap
IMHO.../rant)
Here's what I think: Amazone DOES get browsers, but you're likely to have your item up there a LONG time, then again, you can name your price.
On Ebay, I think you have a higher likely hood of moving it in a week or so if you're reasonably priced... and you might get lucky and get a newbayer bidding war.

I think for our niche, either alt.
rpg.marketplace on Usenet, a posting here or on ENWorld or Ebay are you 3 top choices for attracting an audience.
Amazon would be like.. pretty close to the bottom I think.
Just my humble opinion.