There's a new study that's come up with a lot of theories about social networking sites that seem pretty common sense-y. I'm a big fan of facebook, due mainly to the idea of photo sharing in such a convenient manner, and I take advantage of the wall feature quite a bit. I send out notes asking for volunteers via the site, talking to kids that I tutor, and I even asked my english teacher (a grad student) if she'd write my teacher recommendations for college applications through the messaging system. The last may have been toeing the line as to social etiquette, but I'm always amazed at how well the younger generation adapt to new sites.
I've got to say, I never really liked myspace, as the only really useful feature when I looked at it a year and a half ago was really the wall space; everything else was pretty superfluous and distracting, though it was clearly the freedom of having "your own space" online to decorate, write junk on, etc that drew most people to the site. Once facebook opened its doors to non college students, the first to sign up were the ex-myspace junkies. These people ran around collecting all of the people they'd ever passed in the halls as friends, and started "keeping in touch" with live (or more accurately freuqently updated) status lines that describe moods, location, activities, etc for all to see. These people aren't really good friends with 500 people that they've hooked up with; most of them probably wouldn't wave on the street. But there's a major politeness issue concerning turning a friend request down, especially if one day the rejected party might need to work with you. There's also an extremely casual way to say "hey!" as though in passing, with scarcely more than a what's-up/not-much sort of exchange. This is an extremely efficient way to shirk your duties of friend-making-time, which the study identifies as a vital step in gaining friendships. However, there's also the set of people that you may need to contact for a group project, that you hooked up with at a summer job, or any other trivial acquaintence that you won't mind checking up with here and there. There's the issue of people who travel, who use facebook to keep in touch with friends and family across the world. (I actually go to school out of town, so this is a big plus for me!)
The ones that I talk with most on facebook, however, are really not my best friends. My best friends live in my dorm, and to a large degree this amount of connectivity eliminates the need for such a medium of communication. The most meaningful parts of my day, as the study points out, are not going to take place on a website, but in my personal interactions with the people I know.
I think I rambled sufficiently. Facebook is fun! It helps people keep in contact in an extremely casual manner, but is really not the method of choice for communicating with people you have close access to (such as those in your dorm...)!
PS: The site also mentions the need for honest communications, which is eased by face-to-face contact. When I'm chatting with friends I have a big issue with being overly sarcastic: it gets to the point where they attempt to force me to italicize my text if I'm intending sarcasm, because it just doesn't transfer properly, and much confusion results. Even phones allow for more transference of contextual information than the text contained in a wall post.