How NOT to use social network services

Recently I've received several requests from acquaintances asking me to endorse their work on social network services such as LinkedIn or Xing. Those are from people that I've met in person, but I've never worked with them! Writing a business recommendation for someone I've never worked directly with would be the equivalent of accepting a direct connection on those services with someone I don't know, which is diluting the worth of those social networks. I'm absolutely amazed to see, right in my own network, people with more than 500 connections (LinkedIn subtly stopped showing the exact number, but I remember that a guy like Loic had something like a thousand in no time!) and I really wonder 1) if they really know all those people, 2) if all those contacts are valuable, 3) isn't their network size becoming a burden at some point?

I really don't blame those who have contacted me, firstly because they thought I could help, secondly because the social network services make it way to easy to send out all sorts of requests with the click of a button. But sometimes I think those services are shooting themselves in the foot. How can I trust network connection and endorsements if they're that easy to request and are distributed like candies?

My policy on social network services is to accept connections with people that I know (that doesn't necessarily mean that I've met them in meatspace, because my notion of "real life" is slightly larger than its normal conception ;-) and to give endorsements to people I've worked with directly.