No offense, but I think a lot of the panicking here is a bit unwarranted. I understand being cautious about meeting people online if you're a teenager, but when we're talking about online dating sites, most of them require their users to be adults, and will ban anyone lying about their age (including both teens trying to pose as adults, and older adults trying to seem younger than they are). I'm a 22-year-old graduate student, i.e., a little too old to be a target of "pedophiles." And it's not like there aren't ways to be careful in case the person you're meeting is not who they say they are, like meeting in a public place you both know and letting a friend know where you are and when you're expected to be back, precautions I always take when meeting anyone from the Internet. (I've heard it's good to also have "code phrases" for your friends in case you're in enough danger that you can't tell them directly, making it something like "water the plants" or "feed the cat" where you'd have an excuse for calling during the date. Luckily, I've never been in a situation where that was necessary.)
While I'm hardly a huge fan of online dating sites myself, I really fail to see how finding someone by carefully perusing a profile and pictures (and the profiles are thorough enough that and people are expected to have multiple pictures to the point that it makes it hard to convincingly create a fake identity) is somehow more dangerous than hooking up with some random person you meet at the bar. At least with these sites, you're given some details as to who they are and how compatible they are with you first, so that you have some idea what to expect. And I have to say that in college, I knew a ton of people who were using online dating sites - it seemed like all my friends had an account whenever they were single - but never have any of the rapes I've heard about occurred as a result of them using those sites. And this is backed up by just about every set of statistics I've read about rape, which say that you're far more likely to be raped by someone you already know than you are by a stranger.
I would say one of the issues with meeting someone online is that so much of communication is nonverbal, and it's really hard to fall for someone just on a list of interests alone, as those sites often have you do. Which is why you eventually need to take it offline at some point. I've noticed a lot of people I've met IRL who are not what I was looking for physically, but I loved them personality-wise enough that it didn't matter. That's a lot harder on a dating site, where I've met a few people who would be perfect personality-wise but they're not physically-attractive to me at all, and it really bums me out that I can't get past that with some people. (Not caring about physical attraction is a nice ideal, but if you just don't have chemistry with someone for that reason, it's not like you can force yourself to like them that way.) I imagine I would if they were more than a list of interests and a set of photos, but that's all they are on OkCupid. You really can't commit to much until you've spent some time with them in the real world, and been able to gauge your chemistry as well as compatibility, as well as seen if their photos are really that great of an indicator of their attractiveness (some people are just really un-photogenic).
It seems to me that online dating works best when it's just one method that you use for meeting people, as has been the case with most friends I know who've done it. People who invest too much in creating online profiles and not enough in going out and meeting people in "meatspace" are the ones who lose out, usually because they lack the social skills to meet people "normally" and think that they can get around that by dating online. The rule of thumb seems to be that if you can't date offline, you can't date online. It should be a supplement to, not a substitute for, your offline social life.