I'll still bust this out if it's some quick page that's not going to last long (like some kind of "service down for maintenance" page that's only going to be visible for a few minutes, or something)

It's "bad" but you know what? It fucking works, it's concise, and I can remember it no matter how long I go between writing HTML/CSS.

Hell I wouldn't be surprised if the paths it takes through a typical browser engine also makes it burn 5% or fewer as many cycles as CSS centering methods.