Although I'm on multiple sites, for most I only post a profile but am not active on them (although I do respond to emails, connection requests and answer a question if I find it intriguing). Where I focus my attention is the big three Facebook, LinkedIn and Twitter. My posts are relevant to what's going on in my business and I use all three daily. For those who don't have the time to be as active, I think the absolute minimum for these sites: LinkedIn twice a week, Facebook and Twitter twice a day. But I don't just write updates, I participate in group discussions, RSVP to events, retweet, etc. If all you do is write an update then you're not connecting with others which is the purpose of social media. So the real question should be, how are you connecting to people on social media?