Blood and alcohol will probably make it M. Maybe they'll introduce swearing in the game? I didn't think there was any in Oblivion, but it was in Fallout so I think it'll be in Skyrim too.
I've seen quite a few T rated games with blood in them (Morrowind, for example.) and alcohol, for that matter (Morrowind has this once again.) so I wouldn't say the presence of blood automatically means an M rating, it depends on how much blood there is and how realistically it's handled. After all, Morrowind's blood was just a puff of red particles you'd see when you hit enemies, it didn't even stick to objects like in Oblivion.
But I doubt we'll see any swearing, it seems to be a pretty common trend in fantasy that real life swears will not be used, regardless of how much violence or six the work has. Obviously, there are exceptions, I seem to recall hearing some swearing in the Witcher, for example, but I doubt we'll here anything stronger than the language we heard in Oblivion.