Going to be Stark Raven Mad in about 68 days :)
Seriously, though - I have not spent much time trying to figure out why coasters fascinate me, they just do. I guess the sensation of speed they give, I mean most coasters don't go as fast as a car on the highway but seem much faster. That feeling when a coaster seems to be trying to throw you out of it, is also one of the things I like, a good solid pop of airtime is the best.
I also find coasters, wooden mainly, to be aestheticaly pleasing, like great big wood sculptures or something, is that weird? I don't know.
Personally I think everybody should have something they obsess over or some kind of hobby, I mean have you ever met someone whom had no interest in anything? they are boring and bland!
(stepping down off my soapbox now)