A post about how Twitter differs from Facebook re networking. This post is from an entrepreneur's perspective, but there are parallels here for researchers and the most agile and adept researchers also use Twitter in much the same way.
Tumblr is a growing social media platform that is a bit of a mix between Twitter, a blog and something like Flickr (as it is normally associated with images or short videos). It is suited to multiple platforms and cloud-based. It is a platform that may suit some researchers. Another multi-platform blog along similar lines is Posterous.
Free professional network for scientists. Has useful tools to help - Connect and Communicate: Interact with fellow researchers and build your scientific network. Share and Collaborate: Post updates, discuss methods and co-edit with colleagues. Discover: Download full-text papers, find conferences and scientific jobs.