I've been shocked at how often I see the Dropbox icon on friend's systems. I no longer live in silicon valley, and so I am completely out of the echo chamber (except what I read here at HN). These are not nerds, not techies, and not people who follow TechCrunch. These are artists, musicians, old folks, nomads, and all sorts of folks that just don't do technology. But, they get Dropbox. Admittedly, my parents aren't using Dropbox, but my parents don't read CNN.com, either, and I can't imagine what they would even use Dropbox for. I can't even get them to use flickr for photos, despite buying them a digital camera (my mom still uses a film camera when she travels because she's afraid she'll lose or break the digital one).
If I could invest in Dropbox, I would. But, that wasn't always true. I met Drew at a YC party before they had anything to show, and were still figuring out the diffing/versioning problems, and all the underlying hard problems. And, I came away thinking, "Well, that's been done before. A lot. And it never went anywhere." I had even built a little web-based file manager and sharing app as a RoR practice app, a couple weeks before. So, I thought I knew a business that wouldn't go anywhere when I saw it. I thought highly of Drew, but not much of the idea. I was obviously very wrong about the idea.
Anyway, my point is, Dropbox hasn't been something "you've never heard of" for quite some time.