Google Docs gets six new fonts, including Calibri, courtesy of Google Font API
Curiously, only the Droid fonts show up in the Google Font Directory, but whether that's for licensing reasons or not I don't know. Perhaps it just hasn't been updated yet.
Anyway, choice is great and all -- they're working on adding more fonts and support for other character sets! -- but the most important thing is that imported Microsoft Word docs written in Calibri will now import properly into Google Docs. Hooray!