TITLE: Any reason I should join ResearchGate?
QUESTION [16 upvotes]: I am getting "invitations" to join ResearchGate. I am not a member of any other social network, as I consider it a waste of time. Are there good reasons for a mathematician to join ResearchGate? Can anybody provide experiences that speak for or against joining?

REPLY [5 votes]: On Academia.SE there is a question ResearchGate: an asset or a waste of time?.
Opinions there are mostly negative (not only not too beneficial, but also can annoy others [e.g. distinguished professors with whom you are collaborating] with emails). E.g.:

As is, I have yet to hear any positive success story from my peers. All I've heard of ResearchGate are complaints about their invitation spam.

or 

My experience with ResearchGate has been negative. I was searching for a paper online, and a ResearchGate page came up. I signed up as a member because they promised to send me a pdf of the paper. They never sent it and instead sent unrelated spam.

That said, as with any social network, it can change over time.
Personally, I would love to have a good profile/networking site for scientists, but it seems that we need to wait.
Or as put by one comment on A.SE:

My personal stance is that RG is a wonderful idea (especially the Q&A parts) which are terribly executed.