Well, Shifter, that's an interesting question, and I think that I, Katy, have some insight here. (People are SO going to think I just morphed into Sybil. Every once in a while you should just post and say you exist--oh, maybe this whole aside proves your point better than mine. I guess I'd better get back to my post.)
I guess the chief reason I'm comfortable with people online is that I know that in person I come off like a total moron. And online (or on the phone), I think I come off as being slightly more intelligent than a moron a fair amount of the time. And, oddly, online it's easier to have a conversation about books or philosophical concepts, because writing somehow lends itself to those conversations more than...actual conversation. At least, that's how it is with a lot of people. The rest of us need to come up with a secret handshake so that we can recognize each other and have these awesome conversations in person.
Anyway, when I'm talking to someone online, I'm often thinking about them the way I think of myself. I often think that I'm talking to someone who's probably able to say things the way they want to in an e-mail or even an IM, someone who might not be able to verbalize their thoughts as eloquently in a conversation. Or I think that maybe we're free to have this conversation, whereas in person we might be horribly distracted by our bodies, which have inexplicably refused to develop toned biceps and ripped abs and whatever other accouterments we think are necessary or attractive. And so in some ways, I think you get the best of people when you meet them online.
Is there more to people than thoughts and words? Well, there's lots more. Some of it matters more than it should (waistline and hairline mean a lot less online). But you're definitely missing at least a third of the equation. The Big Three are thoughts, words, and deeds, and without the deeds, there's a lot you don't know. And truly, you have almost no guarantee of accessing a person's deeds online. Unless there's a story about them pulling a baby out of a burning building in the New York Times when you google them, you're at sea. And even then, you know what they were like (via their deeds) for a ten-minute stretch of their life. In the scheme of things, ten minutes ain't much.
Still, I've worked virtually with a lot of people. I've worked with some folks for years before I've met them, and I have to say that if you trust yourself, you're right more often than you're wrong. I've been wrong a couple of times, and they've had some bad consequences. But I've also been right a lot, and gotten some solid friendships in the bargain. Not exclusively online friends--these are people I've talked with every couple of days for a few years, working on a joint project through good days and bad days, all without a photo or anything other than a voice on the phone. Then I've met and spent extensive time with those folks in person, in real human time. These people have seen me in exactly the situations you seek to edit out of your life when you present it online--with stripey tiger hair after a bad visit to the hairdresser, or after the worst, most harrowing evening of your life when you don't think you'll ever stop crying. And when things were bad, those people's deeds typically matched up with their words.
Admittedly, people are probably slightly less likely to lie at work than in an online game, but I think the principle is similar. I've also met non-work people after lengthy correspondence online and found them pretty much exactly as I expected to find them, but more, if that makes sense. There's the aspect of them you're used to relating to online, and then there's all this extra stuff. You get "Intriguing Person X," and then as a bonus, you get infinitely more "Intriguing Person X." And this person is intrinsically more like the person you met online than ever before, and also intrinsically different--endlessly surprising, with extra communication quirks, with holes in their socks and threadbare elbows on their favorite sweater, and also an unexpected scorn for modern architecture, an endearing way of talking to the car when they drive, and an appalling propensity to get lost when driving in a perfectly straight line.
This all sounds idyllic, and indeed, it is. But I won't lie. Sometimes the person veers suddenly into talk of wife-swapping and decides to arbitrarily disrobe in the middle of a perfectly innocuous conversation, and escape becomes your only thought. And it is dangerous to give in entirely to the notion that we can know people without at least some direct knowledge of their deeds. But you can be a lot smarter about it than I was. You don't have to get into someone's car (turned out okay, apart from his questionable navigation) or to someone's hotel room (both very good and very bad experiences here).
But here's where I think we differ. Despite being labeled a pessimist by virtually everyone who knows me, I really do have a deep and abiding desire to believe the best of people. For the most part, I think you get the best from people this way. (Actually, I think you always get the best from people this way--except that for some people the best is really, really bad. I'm sure Hannibal Lecter's at his best plating up a victim, but how good is that, really?) So I'm okay believing that the person is who they say they are (while not giving them my address or credit card information or anything else that seems like it might end up being discovered in Act II of "Without a Trace"). I think it would worry you that the person was a creep, even if you were guaranteed that they'd never wage creepiness on you and even if you were guaranteed that the creepiness would never come to anything significant.
And for the record, the folks I met online often had more reason to be afraid of me than I had to be afraid of them. It was at least as dangerous for that guy to let me get into his car as it was for me to get into it. Yeah, sure, I know y'all are testosteroney and naturally dangerous. Fine, you're all born fighters. But for all he knew, I could have had a gun and a burning desire to collect his ears in a bucket. We both lucked out.
And in the end, how well do we know people, anyway? I'd stake my life on certain ideas I have about you, but the more I get to know you the more certain I am that I can't predict your response to lots and lots of ideas and situations. I think it's fair to say that people never lose the ability to surprise us in good and bad ways, no matter how we meet them or how well we think we know them.