My incredulity stems from the inherent contradiction in the linked article, where the author not only slams Microsoft for lacking a social component in its email, but also for not making its software simpler. An email client is very simple: it allows me to have asynchronous conversations with other people in plain text, and keeps records of what's been said. Adding a "social" element doesn't make it better, it just distracts from the simple act of communication.
I completely agree that Facebook is an invaluable way to keep in touch with people, in both personal and professional contexts. But staying in touch is a different sort of interaction than having a precise, nuanced conversation. Communication isn't homogeneous, and just because Facebook is good at one kind doesn't mean it's the perfect medium for all communication. Anyone who says differently has drunk too much kool-aid.
Personally, I haven't replaced my work e-mail with FaceBook messages yet, or started using Events for business meetups (though there is a news.YC FaceBook group, and I wouldn't be surprised if some of the news.YC meetups are on there). However, there've been times I've been called up by a college classmate, in a business context (he was doing market research for a hedge fund client), when he said "I got your number off FaceBook. It's pretty handy for that." Another friend (also at a hedge fund) told me over G!Chat that "One of my coworkers is into webstartups. Shoot him a FaceBook message and see if you'd be a good match for each other." When my cofounder quit and I was searching for a replacement, I sent one of my former coworkers a FaceBook message to see if he was interested.
I get the impression that most people my age (2-3 years out of college) don't really know what to make of social networking in a business context yet. I get a lot of panicked notes saying "My boss friended me on FaceBook. What do I do?" Some people are shutting everyone from work out of their FaceBook accounts because they really don't want their boss seeing the photos of the drunken revelry they had last night. But others are using it like an online Rolodex & e-mail client, which it's always sorta been. I think it could go either way. It's certainly not as cut-andd-dried as your incredulous reaction suggests.