I have gotten lots of recruiter emails saying they saw my LinkedIn profile, which is kinda funny, since it doesn't exist.
Could just be the kinds of jobs I'm interested in.
I personally think that for software dev at least, making connections via Twitter or via friends is a better way to go for the first internship, but everyone has different paths to success :)
"Can't risk" is interesting, you could say that about anything you could put on your resume if there's a chance it helps, but something like LinkedIn seems just redundant with your resume's content.
So people definitely use it, even if it isn't on your resume.