I have a pair of Shimano MO-somethingortheother (like Rev. said, they keep changing numbers). They don't easily scratch floors, but it is possible to hear the cleat click occasionally when e.g. climbing stairs. So they can be slippery on wet, hard surfaces. Also, due to the stiff sole, they are not nearly as comfortable to walk in as almost any other shoes I have. But I suppose you have to compromise a bit there.
--J