I have a Facebook page. I don't think that Facebook in itself is a line the faculty shouldn't cross. Thanks to college and graduate school, most of my friends are scattered around the country, and we use Facebook to keep in touch. I post very little personal information (as seems more common among people my age who are older than our students but younger than our colleagues) and what I do post is limited to favorite books, music, etc. that might be edifying for students to look up, should they stumble upon my profile. That said, I think it IS inappropriate for professors (or other professionals) to post pictures of their drunken parties, both because it may undermine one's authority in the classroom and because it doesn't model an appropriate, professional use of social networking tools. If we're going to tell students not to post pictures or information they wouldn't want future employers (or their teachers) to see, then those of us using Facebook should set the bar high.
I think the professor described in the post is crossing a line. As in real life, I would never be "friends" with my students on Facebook -- perhaps with alum, but not with students. I think that kind of relationship, even if the professor can keep it straight, is potentially confusing to students. They may end up not sure how to interact with the professor in class, and certainly future students -- who have heard how "cool" the professor is on Facebook -- may be confused if the classroom version doesn't add up to what's online.
To choose an image of oneself that seems clearly aimed at making students think you're "hip" and "fun" -- anything involving alcohol or parties, any mention of hot dates, in short, anything you used to brag about when YOU were in college, and to so clearly put that image out to your students by being their "friend"... we get it. You want your students to think you're cool. You're hoping Facebook will give you some street cred. But your students are not your friends. After this semester, when the grades are in and you gave them the D they earned (or didn't, because they were your "friend" on Facebook), that student will probably not be your "friend" anymore. Heck, they might even dissolve your Facebook friendship. And they would be right to, because most of them -- whether they know it or not -- are just using you, allowing the boundaries to get blurred so that you DO feel badly about failing them or generally being a hard ass.
The other, more pedagogical, problem with heavy use of Facebook between students and faculty, is that it can allow professors to be far too available to students. I've heard of people using Facebook as an extension of IM, so that students can quickly ask questions and get a response. But honestly, I don't WANT my students to post questions about MLA citation on my wall two hours before the paper is due -- not because it crosses a boundary, but because I want them to be learning to find the answer on their own. I don't want my students to know that I'm updating my profile right this very second and therefore could be poked so they can ask what they missed in class today, simply because I don't want them to get the idea that I will always drop everything to deal with their problems. I won't, and when that day comes, I don't want my student to have thought I would always be accessible.
A professor like the one described in the email risks a lot. Do you really want students (or your dean) to know that you have a glass of wine while you grade their papers? (Evaluation: I got an F because he graded my paper while he was drunk). Do you really want them to know you're planning class twenty minutes before it happens? (Evaluation: Teacher isn't prepared). Do you want them to know where you are and what you're doing when you're ignoring their inane emails? (Evaluation: Teacher is difficult to get in touch with and doesn't answer email promptly). Do you really want them to see it if the prof across the hall from your office, or your real life friend, writes something snarky on your wall about your most precious little snowflake, about whom you have been complaining a great deal?
But in the end, it's just kind of sad. I think it's totally ok to have professors on Facebook, just as professors may go to the same bars, coffee shops, etc. that their students frequent. It's a social gathering place, of sorts. People will be there. But to INVITE your students to the bar or coffee shop is something else... it's confusing the social/professional boundary, but it's also a little pathetic. I think of Facebook like my local bar. I go there with my friends, and if I run into an undergrad student I quickly make necessary small talk and then try to avoid that student for the rest of the night. If I were to buy that student a drink and ask him to dance, I might be cool for awhile, but it's cool with a big side of creepy. After all (this is the part that professor seems to be missing) if you were really that cool, you wouldn't HAVE to be friends with your students on Facebook. You'd have your own friends. Cooler, more intellectually stimulating friends. Your own age.