"Enthusiasm for tweeting about everything that goes into, and comes out of, your body" = my favorite part.
I don't have a problem with LinkedIn's endorsement system. I think users think they're doing something nice for their friends by endorsing them. But employers and clients probably don't really take the endorsements seriously, so they end up being online noise (like YouTube and newspaper comment threads, which is one of the points you're making here).
I was thinking of someone who tweeted "I really need to find a bathroom!" Then put down your phone and go look for a bathroom--I don't think anyone on Twitter will help you with that. (In addition to the usual, "here's what I ate for breakfast" tweet.)
I do endorse people on LinkedIn when I know that they have that skill because I've worked with them on that particular topic; in that case I agree it's a nice thing to do. A lot of times, I know that skill is part of their job, but if I haven't seen them do it, I don't feel qualified to endorse them. I guess I'm missing the point by not just blindly endorsing people...
I don't have a problem with LinkedIn's endorsement system. I think users think they're doing something nice for their friends by endorsing them. But employers and clients probably don't really take the endorsements seriously, so they end up being online noise (like YouTube and newspaper comment threads, which is one of the points you're making here).