I first read about RP in August 2007 and it brought me out of my complete apathy for political policy. I was totally on-board from then on, but even as recently as January 2011 I still felt that discussing politics was pointless because I felt it was divisive and that most people are unwilling to change their minds. Around that time, I ended up having a few discussions with 1 vocally liberal friend and 1 vocally neoconservative friend and they both felt that talking about the issues helps to flesh one's own ideas out. So I began posting, discussing, and arguing policy with people from both sides on the fence on Facebook on a regular basis, but primarily for selfish reasons.
Lo and behold, in the past few months I found that I've actually made an impact on a few friends. One friend who was completely uninterested in politics (somewhat of a fan of Obama though) recently became a rabid Ron Paul fan! Another friend who was super neoconservative (told me last year that the middle east hates us for our freedom) is now a big fan of Ron Paul too! Also, a few of my extremely liberal friends have become more supportive of states rights and imposing their agenda at that level rather than a federal one. My most recent FB posts have been getting more likes, and other friends who are a little hesitant about Ron Paul have been asking me detailed questions about his positions. I've also had a few acquaintances approach me in person and talk to me about my Ron Paul posts, but they've never liked or commented on any of the posts on FB. I don't claim to have been solely responsible for any of these people's interest in RP as I'm sure the recent surge in RP's supporters has helped, but I am certain that my posts have at least been food for thought.
As a result, I no longer believe that it's pointless to discuss politics with people. Some people may be unwilling to change their mindsets, but most will continue to adapt their beliefs in the face of new information, even if it's in by very, very small and gradual measures. I think the key is how you approach the discussion. It is critical that you spend more time explaining your viewpoint rather than attacking theirs, and it is also helpful to acknowledge the valid points they make. Some people pick a side and immediately vilify EVERYTHING the other side says/does, but that type of "with us or against us" thinking just turns the discussion into a battle rather than comparison of ideas. If you turn it into a battle, the other guy will shut off the learning part of his brain and will instead focus entirely on protecting his ego and trying to "win" the argument. In my opinion, that type of political discussion has no value whatsoever!