First off, Aloysius is conquering the legions of steampunks online and corraling them at the Steampunk Ning Empire. Events, photos, a forum, and much more are to be found! (He's a benevolent tyrant, so it's okay. I recommend you join!)
More events taking place this year include "Sphinx & Drinks" at the Egyptian Rosicrucian Museum in San Jose this July and WindyCon(featuring a steampunk theme this year) in Chicago this November. Start planning now!
You know steampunk is getting mainstream when there are actual "steampunk jewelry" suppliers online, by the way. Not that I'm complaining, as I'm one of the types who want this look and art in the mainstream so that it's easier and cheaper to find!
These steampunk rides, on the other hand, will never be mainstream, but they are amazing and worthy of wonder for that very reason.
And finally, for those of us who also love the 1920s, 1930s and 1940s: Dieselpunks!