Which social networking apps should you 'friend?'

[1]Facebook is still growing strong and Twitter remains all... er, a-twitter. And, according to CCS Insight Research, one-third of users between the ages of 16 and 35 regularly access sites like Facebook and Twitter via a wireless device. But there is a range of mobile social networking offerings beyond the well-known brands, those that serve either niche purposes or fill in the gaps the better-known apps don't cover. Slideshow [1]