I have to echo what everyone has said since kilee moved the thread here. General feeling among Disney pin collectors is carry-on over checked luggage. If they're in your checked luggage and the luggage is searched, there's the danger that something could happen and the pins could be lost.
Last time DW and I flew to WDW a few years ago (man, has it been that long??), we had our pins (including a couple of books of traders and a large amount for lanyard trading) in our carry-on. Before the bag went through the scanner, we let the TSA agent here in Richmond know about the large collection of lapel pins in the bag and that they'll probably want to hand-check it, which they did. It wasn't that big of a deal and the TSA agents were cool about it. As Safetymom said, so many go through MCO that security will just wave you through.