As someone who grew up on the east coast spending hours as a kid chasing around fireflies, its always been weird when I find someone who has never seen them before. It seems like that might become more and more common, however, as experts are reporting that firefly populations are dropping significantly. In fact, populations are down as much as 70%.
Possible causes include urban sprawl, industrial pollution, and artificial lights. It doesn't say it in the article, but I'm going to guess that global climate change isn't helping these little guys.
Fireflies seem to be just the most recent in a long list of species that are in declines, from honeybees to bats to amphibian populations, it seems like more and more species are in serious trouble.