User blog comment:XvLIGHTNINGvx/Some minor Skyrim details from Pete Hines/@comment-4118895-20110914010844/@comment-2189407-20110914021350

There are three autosave slots instead of one which I assume it will save over the oldest one, autosaves happen on traveling, sleeping, and waiting like in Oblivion but you can also set intervals for autosaves so it will happen automatically every five mionutes or whatever you set it to (useful when wandering the wilderness) and you can still save normally anywhere you please.