On the one hand, it's another distraction. As Paul Graham wrote, the ability to carry the internet around is not necessarily a move someone aspiring to get more done should make.

Maybe a valuable smartphone app would be one which blocks your web browsing access unless you explicitly request a five-minute unblock -- and gives out larger intervals only after making you click through an irritatingly long series of "Are you sure you're sure?" dialogs that jump around the screen so you can't just tap on "OK" repeatedly. Not enough to cripple your phone, but enough to make you think twice about idly rechecking your email for the 18th time today.