A few people have emailed asking how to make the little fabric-covered tacks I posted previously. See step-by-step photos below, going from left to right.
Start with a pack of "Wedding Gown Size" (size 20, 1/2") metal buttons to cover (available at fabric stores for about $1.50). Pull the loops off all the button backing pieces with a pliers or wire cutter. Cut your fabric scraps into circles slightly larger than a quarter, or use the circle template printed on the back of your button package. (Since the edges get tucked in under the metal backing, you don't have to be a careful cutter.)
Following the package directions, use the "pusher" tool that came in the pack to cover your buttons with fabric. This step is easy and the most fun! Then use a generous amount of hot glue to attach a tack to the back of your button. A standard tack should fit perfectly. Your cork board will thank you.
UPDATE: You can buy buttons to cover that have flat backs so you don't have to yank off the wire loops! I didn't know this when I made mine. Shoot. Could have saved myself some work. (Update to the update: that link is expired now, but I bet you can find them elsewhere.)