I ran into a blog that discusses the issue of the "creepy treehouse." What this term refers to is adults trying to lure children in by making something look like fun. In the technology world, this is being applied to adults trying to create stuff for young adults, such as librarians and educators getting involved in MySpace and Facebook. See Barbara's post for a more eloquent explanation.
I have heard reports that performed surveys of college students and very few wanted librarians involved in Facebook. They see that as their space, meant for socialization, and they don't want us stalking them there. So many librarians are talking about using social networking tools to "meet the students where they are." I haven't bought into that. I mean, I don't want anyone bothering me there unless I ask them to. I do use these to keep in touch with friends from grad school. Some students here have chosen to make me their friend and invite me to join groups, but only two students have ever contacted me that way and it wasn't for anything library-related.
I don't see anything wrong with making Facebook widgets available since you can do so much with the same widgets in other places. I definitely don't plan to stalk down our students through these means, and now I have a great term to back up my excuses!