social networks for scientists. are they useful?

I have recently stumbled on  several websites  that can be described as “social networks for scientists” .  Although I’m not still convinced of its usefulness I have compiled a list that I present below.

What I propose is that we can all check them out and afterwards discuss if this kind of web tools are really useful or if is just more noise to had to all what is already in the internet (like this blog, for instance   ).

My first question is: what does this bring of novelty for suggesting  papers to collaborators or starting new collaborations and discussions? Can’t we do all of this just as easily just by using e-mail?

My second question is: is it an efficient way of promoting your work and your papers in order to get more citations by having enhanced visibility? Having a good personal webpage where you can give a nice overview of your work and publications is not more straightforward than being registered in I don’t know how many sites that you won’t be able to update conveniently?

Here is a list of just a few examples of this sites (probably the most interesting):

https://www.researchgate.net/

http://www.biomedexperts.com/

http://lib.bioinfo.pl/

http://www.2collab.com/nonLoggedInHomePage

http://www.labmeeting.com/signin

http://www.discover8.com/

http://www.scilink.com/start.action