Steampunk is all about the design and very little concerned with added (or lost) function but some of it would be neat if it worked half as well as you wish it would.
That's about my take on it; my aesthetic sense says "ooh, shiny" and "mmm, leather" and "lovely scrollwork there, that would be fun to make" and my engineer side says "but...but...shouldn't those gears be doing something?"
In any case, The Kneeslider has a piece on steampunk motorcycles, including the Hubbard Steamcycle, which may eventually actually run on steam, and a German bike that's a one-cylinder, 1440 cc machine with a shovel for a seat.
Several other steampunk (or even steam-engine) bikes are mentioned in the comment section, as well. The 1908 Field Steam Bike includes "To progress gently move cut off lever and PRAY" as step 10 of the startup procedure, and this sleek little machine would be perfect for any aspiring steampunk supervillain.
And from the nigh-venerable Steampunk Workshop, a piece on Tom Sepe's Whirlygig Emoto, a beautifully-crafted "electric-steam hybrid motorcycle."