As a corporate worker for years, it seemed that this was more prevalent in the upper management areas where directors, VPs, the "Crackberry class" always wanted to know what was happening.
And like everything else, they succeeded or failed wildly. Some can handle two things at once and some couldn't.
But more, they never had a life, being too connected. That was one thing I hated and refused to get a Blackberry for that reason. I don't like being "live" on the network all the time. There's a time for it (when I'm on call), but many other times I want to work on something else. We even had a wireless service inside the campus where your desk phone would be forwarded to your cell phone anywhere in the building, which worked great in the data center. But when I'm away from my desk, I usually don't want to be interrupted because I'm doing something, so I never used it.
I see this at home as well, and as mentioned in the other posts so far. My wife will call me like 4 or 5 times on the way home, for these little snippets, "did you hear?" or "stop and get this" or "what about this?" and it's annoying.
The mobile phone doesn't mean that we are always available. It's a tool and should be used as a tool when appropriate. Not for every little whim or distraction.