A lot of light-duty users are already shifting to phones or tablets as their primary Internet device. A similar shift already took place in 2008, when laptops started outselling desktops. They are "good enough," but phones will never replace laptops which will never replace desktops for simple reasons of physics: Space and power.
No matter how good the processor in a phone gets, a laptop can have ten of them, and a desktop fifty (or the equivalent in fewer chips). Anything a phone or tablet can do, a laptop or desktop will be able to do faster. Until someone comes up with a micro-fusion reactor that produces unlimited power in nearly no space and weight, larger machines have a permanent advantage.
I think Apple is onto something with Siri -- not the voice commands, but the way it processes them. The phone is essentially a terminal that offloads the heavy processing tasks to a remote data center. Even with fast networks, that won't do for anything that requires real-time responses, but it could expand the tasks available for portable devices.
“I think Apple is onto something with Siri — not the voice commands, but the way it processes them. The phone is essentially a terminal that offloads the heavy processing tasks to a remote data center.”
That’s nice if you live in a metro area but those of us in fly over country and flaky coverage want as much happening locally as posible.