Beer Coaster Collectors Unite!

So how many of you out there collect beer coasters? My father is a rabid collecter of them. He started in the Air Force and just started adding to the collection over time. I attended conferences and beer memorabilia shows as a youngster so I know there is a niche. There are lots of folks here in America and abroad that are into this... but how many? I am curious how far reaching this universe of collectors is. Drop a line if you collect and how it became your passion.