ResearchGate is a social network website for researchers. It’s something similar to LinkedIn as to business people/professionals, but RG is geared towards researchers and scientists. ResearchGate lets you connect to other researchers, and let you upload the publication so that other people can download.
I personally find it useful. I host my workshop paper here in my blog for downloading, but I don’t seem to get any traffic. But since I uploaded it to RG, that paper has been downloaded several times. It could enhance my academic impact, I think.