Knowing how these things go when a game is released on console and PC, it would be quite unusual for PC gamers to be able to play alongside console gamers. As Diablo 3 will be utilising the Playstation Network for online play there will be no connectivity between that and Battle.Net. Also, the games are quite different with different interfaces which will impact the gameplay. Just to confirm this Blizzard have issued this comment:
In terms of allowing an analog controller hookup for the PC, we don’t have any plans for that kind of support right now. Similarly, since Diablo III for console was designed with a controller in mind, the PlayStation version of Diablo III will not support USB mice or keyboards.
At the risk of being abused by console gamers, I will say that nothing can beat a keyboard and mouse 🙂