I've seen a fair bit of evidence of shady players (most of whom seem to be recruiters) on LinkedIn.
I recently got an invite from someone who had crafted their profile to strongly suggest they had worked at a previous employer, and you had to look pretty closely to realize they didn't. Either he was a shady recruiter, or an even shadier player -- definitely a profile which took me several minutes to look at against who I thought it could me.
I have a fairly firm policy that if I don't know you, I'm not adding you. So all those recruiters who are obviously recruiters get ignored.
But the ones who have carefully crafted a profile to mislead you into thinking it could be someone you know, those are much more worrying. I even saw that one of those misleading ones had been added by someone I did formerly work with, because it was a good enough fake that people would fall for it.
This has always been a problem with social networks in my opinion: if the goal is to collect as many links as possible without actually stopping to think of "just who the hell is this person again?", then people are going to be suckered into linking to people they don't know at all.
So you pretty much have a platform in which people are trying to expand their network, and don't seem to think critically enough about just who those people are and if you really want a random recruiter or someone you don't know in your network. Me, I've pretty much decided that I won't link to people I don't actually know.
So, am I surprised to see stuff like this? Not hardly, because in a lot of ways LinkedIn is as much of a pest on the internet as Facebook and Twitter. And if fooling people into adding you into their network gives you a way to fool more people, it's all the more reason to look at those invites and ask "who the fuck is this and why the hell do I care?".