First I have to say I hate the name - I can't help thinking that it sounds slightly obscene, especially because it's a "social networking" site. ButI know I can't possibly be the first person who's made that observation.
I watched the tutorial, and I can see that it does have good applications, especially for research. It's a good way to connect with other people doing the same research, or having the same interests as you. I clicked on different bookmarks and read the comments.
I wasn't inspired enough to set up my own account at this time (mostly because I don't have the time right now), but maybe I will in the future.