Not entirely true. At least in the Bay Area, I've seen some highly targeted ads on my Twitter stream. Twitter also does a great job at showing me ads based on who I follow. Do I act on these ads? Sometimes yes. Companies throw out incentives to act on promoted Tweets. I think it's a nice, subtle form of advertising that just works. Facebook, I don't like. Their advertising comes off very intrusive and honestly, I've never acted on a single ad there. Helps with brand recognition though. When I see a brand advertised on Facebook, I recollect it. How many times have you been to a coffee shop and seen posters redirecting you to their Facebook presence (I know that's not an ad but, it goes to show you that they have a presence there). Some take it to the next level and advertise too! I've seen quite a few local ads on my stream.