I like this line in the submitted article: "But to value every company as if they are the next Google, rather than valuing them all as if one of them might be, is pretty much the definition of a bubble." I think there is insight in that. Not every big new online service can have the long-term revenue growth and user engagement that Google has managed to achieve. (Some of the stories about Groupon point out aptly that Groupon spends much of its revenue on Google promotions, so who is the winner when Google, a profitable company, is paid by Groupon, a company that is losing money on every sale?)
That said, Facebook is the one online service that gets more engagement from me, by far, even than HN or all the Google properties other than Gmail. Facebook's algorithm for prioritizing posts from friends into my home page works amazingly well at showing me the content I want to see. The Facebook secret groups feature works well for me at forming more tightly knit communities. All in all, what's cool about Facebook is that I see FRIENDS there, people I'm glad to see in real life or online.
Back when nobody needed to buy floppy disks, because AOL was endlessly mailing those out to everyone in America, I was subscribed to AOL for a while. I couldn't understand why people preferred the chat-like user discussion interface of AOL to the more threaded discussions available on other online services at the same time. I found AOL rather tedious, and eventually unsubscribed, but millions of users stayed on AOL long after I thought it had lost all of its competitive advantage over other ways of getting on the Internet. AOL had the financial strength and reputation to take over (and drain of value) Time Warner, and it still hasn't completely disappeared. I think Facebook will do at least that well for at least that long. Maybe Facebook is already in a long decline, but it will be a long, slow decline.