Like Matt and cajunscot, I wear my lapel pins on my jacket/coat lapel (or other appropriate location when not wearing a jacket) one at a time, for specific functions. When I wear one, it's usually an Eagle Scout related pin (either the Eagle by itself or my National Eagle Scout Association pin). I also have a pin from my high school, a cross (from my senior retreat), and the BSA fleur-de-lis. I hardly ever wear any of those.

I also have an Eagle lapel pin on my band Glengarry, in front of the clan crest.

That said, I have seen convention-goers and/or tourists wearing multiple pins, likely representing the number of conventions attended.