I've been a huge pin collector for many many years. It goes way back before I went to Disney. I started with ski resort pins, then Hard Rock Cafe and Planet Hollywood pins. Then I went to Disney and was completely hooked. I don't go crazy, usually only 11-15 pins per trip. I only get ones that I like and also special event ones that I've attended, things like that. Last trip DW started getting into to too. She traded a few times with CM's, but I haven't gotten that far yet. Though I do like what someone said earlier in the thread. Either buy a new one or get 2 of ones that are cool so you can trade. Before our next trip I plan on getting a bunch at mousepinsonline.com. Good selection and great prices for trading.
DTD has a great pin store and I also like the store in Frontierland dedicated just to pins. Lots of good stuff there.
I have all my pins on a pin trading vest I bought during my first visit to Disney. Its starting to get pretty full.
Don't forget that if you stay at a Disney resort you get a voucher for 1 free pin which you can pickup at checkout counter of your hotels store. This pin isn't available for sale in any of the pin stores in the parks. Last year I got 2 (we had 2 rooms) apparently there was a set of 5 Disney Bus pins so I got me 2 of them. This year I got the Mickey with a video and still camera (this has turned out to be my favorite thus far as I'm a big photography nut).
Can't wait for the next trip hopefully next year!!