I will allow, but not encourage it. I am not a fan of electronics at the table, as many players in my experience allow themselves to become engaged more with what they can access electronically than with the game at hand.
Some will say that's the GM's problem for not making the game compelling. I think that position underestimates the power of the clicky-zone, and its interaction with human psychology and neurological reward systems. I know people who are so addicted to the online world that, even when out to a fancy dinner, they will excuse themselves from their real-world friends, real-world conversations, and in-person social interaction to go to the bathroom and futz on Facebook for 20 minutes or a half-hour.
One player in my Deadlands game uses a dice roller on his smartphone, and that's no problem whatsoever. Another used to use a tablet for his character sheet and spell listings. The latter tended to get distracted by his e-mail and such, but it wasn't too bad.
In a Star Wars game I played in (I didn't run it, but did host it), out of six people my wife and I were the only ones who didn't have a laptop or tablet at the table. For one player, this made her attention to what she was doing so weak that I was tempted to have "something wrong with our router" so that she wouldn't have internet access during games.
In general, I find that if a game *needs* electronic support, that makes it so rules-fiddly that I don't want to run it anyway.