>It's a truism of cyberspace that when you finally meet an online acquaintance they never look like your mental image of them.

There's more to it. I've had dozens of such encounters, and every time when I had a mental image, it was completely different from the person. Actually, the person was usually a disappointment, "there's no way (s)he looks like this". Not that the looks were bad, it's just the frustration at the failure to match the expectation.

Then only a minute later, the mental image fades into void and I have a feeling that there's no way this person could look anything but what I see.

Strange. Yet it works every time.