I think I can see what's going on really when, but only when I'm a bystander.
Like when two people are talking I will know exactly what the other one means and is coming from, etc. And because of that I also see it a lot of times very obvious when two people aren't on the same page, while they haven't figured that out yet. Sometimes I think I should say something to them about it, to explain what is going on, but then I back off from that, always.
When I'm one of the participants it's quite a bit harder. People I know I can read reasonably well. But I tend to be quite naive with them, so they can easily fool me (jokes), etc.
With people I don't know I guess I'm really sensitive/cynical as my first impression of pretty much anyone I meet is "what a douche...", even with the people I end up getting really close (those few and far between). Because of that I don't tend to trust my gut, which actually sometimes has led me into quite the opposite behaviour of being to naive (though I do think naivity is a good quality, rather then being cynical).