Is this new or I was not aware of it? Google Docs has an option in file menu... "Document Settings". It lets you set the default font for the documents.

http://lh4.google.com/image/hjr.photo/RgAFXibFkiI/AAAAAAAABYs/Rn2Jsg7OVM0/s640-h/new_docs_settings_option.jpg

[ URL edit – Ionut]