A: "Dude, let's go to the arcade and play some DDR!"
B: "Can't, man. I'm broke. Wanna go play some Stepmaina at my house instead?"
A girl who cannot play DDR because she is wheelchair-bound will often own a copy of Stepmania on her computer to get in on the action.
Files for the game (called stepfiles) are user-made, and include a .sm (StepMania's native file format) or .dwi (Dance With Intensity's native file format), a sound file (usually mp3 or ogg) and usually a set of graphics for the background and select screen banner. Some programs, including Dancing Monkeys, have been made in a attempt to make stepfile creation automatic, but files created by these programs are universally accepted as CF (or crap file, a reference to what began as a inside joke about Cobalt Flux metal pads, which are known by their high quality).
StepMania can also emulate Pump It Up (PiU, five panels arranged in a cross-shaped pattern) and ParaParaParadise (PPP, five arrows arranged in the forward, left, right, up-left and up-right positions). The StepMania codebase was used as the source for In The Groove (ITG), a four-panel dance game infamous for its competition with DDR. ITG is now owned by Konami, the producer of DDR, due to a recent lawsuit against Roxor, the producer of ITG.
Not as much as I do. SM is The Roxxorz.