I got an e-mail purporting to be an invitation to sign up for researchgate, which is an academia.edu type thing. So I went ahead and filled it out and clicked on my papers so they would show up.
Today people that I've co-written are getting e-mails saying that I invited them to sign up for researchgate. This is false. Please don't sign up for it. I should have read the wikipedia page, which ends in the following:
ResearchGate has been criticized for emailing unsolicited invitations to the coauthors of its users. These emails are written as if they were personally sent by the user, but they are sent automatically unless the user opts out, which causes some researchers to boycott the service because of this marketing tactic. A study published by the Association for Information Systems found that a dormant account on ResearchGate, using default settings, generated 297 invitations to 38 people over a 16 month period, and that the user profile was automatically attributed to more than 430 publications. Furthermore, journalists and researchers have found that the "RG score," calculated by ResearchGate via a proprietary algorithm, can reach high values under questionable circumstances.
On their help page they say that they will delete your account if you e-mail them and ask. I'll report back if they actually do this.