A couple of days ago I created an Linkedin account. Rocío convinced me to do so, because apparently "everybody was there". I did not really think that I could find anybody there, but after importing all my GMail contacts, it turns out that everybody is actually there.
From a technical point of view, Linkedin does not seem to have any better technology than Facebook or other thematic social network sites like Mendeley (for research). For instance, when browsing the list of contacts of someone else, or when searching for a list of contacts, with the goal of cannibalizing her contacts, if you add someone, you will be redirected to a new page, and you will loose the list of contacts of the previous page (this is, it does not implements HTMLHttpRequest). In general, it lacks many Web 2.0 features.
However, it has become very popular among companies and professionals. Maybe because companies are very conservative and like obsolete technologies, so people feel like at home. Well, I know Linkedin targets professionals and companies, but it is surprising they are not trying to improve the user interface, and remain popular even with a so arcane web.
I am not sure whether it will be any advantage from a professional point of view, but just in case I added as many people as I could. I might probably have missed someone, so if I know you and you are in Linkedin, please let me know or just add me to your list of contacts. This is my public profile.