In the responses, there seem to be 2 approaches to a social network for researchers:
• Use a big network (you mentioned ResearchGate but not GoogleScholar, AcademiaEdu... ?)
The idea of ResearchGate is compelling. Its focus is on publications (with infos, fulltext, citations, & cited by), the link to the researcher's profile and possibility to follow.
• AND/OR use federated services to get similar features (see 2nd post).
@tio @futureisfoss @humanetech @VictorVenema @mpjgregoire @socrates