I completely agree with that, but the reason I use facebook/myspace is to stay in touch with people that normally you wouldn't continue a friendship with. I have a ton of friends from previous work/school & it would be impossible to call all of them up when we never had that kind of friendship. But, we still care about each other & can casually write & keep in contact. I also have an anxiety problem, so I often can't call even my closest friends. (I have to write down the reason for my call LOL but, once I actually MAKE the call, then I'm all good ^_^ ). Anyway, I prefer email/ face-to-face but sometimes that's impossible ^_^ And, as you collect all these people & see that you have 100 contacts you normally wouldn't have, it's definitely an overwhelming thought to go back to the more traditional way of actual communication.
But the adage is totally right; I mean, you're putting yourself out there, so don't be surprised to see yourself, well, out there ^_^
My advisor told me that employeers now adays will actually check for facebook, twitter etc and to look professional, I should have them - I started a twitter account JUST for that reason. (I HATE twitter!) {Someone in an internship said his job was to check to see if those applying for the job had at least 50 people following their twitter account!} So, now when they search for me, they get a nice professional page. But, then I see people with really classy jobs and really inappropriate pages! It makes me think if employers really check as often as my teacher said....
Enough from me LOL sorry, I'm chatty =P