I can think of several 2D games which use the Accelerometer successfully, but in my experience as a player, character control in a 3D environment tends to be frustrating. Mostly because a 3D environment often involves a wider, continuous field of view which prevents me from sitting comfortably while playing.
Is this an unfair generalisation? Are there examples of the Accelerometer working well for 3D games on mobile devices? There is the obvious tradeoff here, screen real estate unobscured by thumbs, but is it worth it?