I think the zombie bubble keeps bursting only to reemerge years later. The same with vampire plots. They are hot for a while, they get over done, then they virtually disappear for years only to come back in a fresh wave.

FWIW, I really loved Zombieland. I thought it brought something new to the table. It was genuinely funny and something new to me. Many of these movies are funny because they are so badly done. It was nice to see one that was all about having fun with the idea.