On the downside, the lack of human interaction 8 to 10 hours a day can make you feel like a troll in a cave. I expect people who have to spend a lot of time on the road may feel the same way sometimes.
Enter Twitter. I started using it before the holidays, and suddenly I don't feel so trollish any more. Via Twitter you can swap jokes with co-workers, get updates on their personal lives, and dip into a steady stream of industry gossip.
You encounter interesting people at random, and now and then someone points to you something cool. These are exactly the kinds of interactions I'd have hanging around the office lunch room or popping across the street to the coffee shop.
It's true that much of the content, mine included, is banal, inane, and/or self-aggrandizing -- just as it would be at the water cooler. Some users post with a frequency equivalent to the guy who can't shut up (Guy Kawasaki, I'm looking at you.) But that's part of what I enjoy about the service -- it's just like real life. Or real enough that I don't miss the office like I used to.
If you're interested, you can follow my banality, inanity, and self aggrandizing talk here.