I had to admit that other than Jules Verne and the time machine, I didn't really understand the scope and prevalence of this genre. The stories take place usually around the Victorian era and generally in Britain. They are an alternative history that always has strange steam powered inventions.
This is an amazingly diverse and entertaining genre. I've learned a lot from bloggers like Andrew Rosenberg whose work Steam Palace I hope to soon see on shelves. A series I eagerly anticipate is The Ministry of Peculiar Occurrences: Phoenix Rising by Pip Ballantine and Tee Morris. Their site is a series of dispatches from their man in Moscow and really shows the voice of the series.
What is amazing about this genre is that there is an entire community that exists around it. From Steam Con, a Seattle based convention to attire and jewelry, Steampunk style incorporates gears and 'mechanisms' with things like crystals.I love the seemingly out of time contraptions that open up the imagination to what is possible. And most of the stories have an altered view of history often with a Victorian perspective.
I can't possibly explain as well as the authors themselves so I encourage you to take a look at their sites.
It's been a pleasure. Now...Go Write!