Sitting at my desk, it's not at all useful. When I'm out shopping, it's nice to have it around to do quick comparative price checks. Inside mall maps are extremely useful (esp Nokia City Lens). When I was in college, I loved being able to check and respond to team emails within lecture. Long travel...helps keep me busy.
I think in general...it's an upgrade from having to carry your laptop around when you're not planning on diving into a desktop app.