I do not think of using social media especially built for academics (academia.edu, RG), but those of the "common" type like twitter and fb.
Increasing visibility of your research through techniques can be used in digital marketing (article marketing, link building, gathering likes, retweets, g+1s and similar). This would certainly influence article metrics and download statistics for OA articles by driving traffic to them.
The thing is that we will not know the relevancy of that traffic, i.e. is it coming from other experts around the world or from a 10-year-old kid who googled "anime" and found the article "Techno-Orientalism and media-tribalism: On Japanese animation and rave culture". If this is so, how and where can altmetrics be useful towards evaluating a researchers' contribution to the field?
Do you have any example or experience of altmetrics playing a role, however small it is, in research performance evaluation?