Also, there have been bitcoiners who are members of those communities (e.g. Reddit, Stack Exchange, etc.) that have suggested incorporating bitcoin into the site itself, but then the fireworks begin.  Some hate the idea as Bitcoin is seen as a threat by some and they go ballistic at the thought of bitcoin encroaching upon their community.  Others hate it because a good reputation on these forums currently must be achieved through merit.  If money gets involved, the type of participation changes and the quality might suffer.  For instance, some think the introduction of Quora credits really hurt Quora, rating it as being not much better than a Yahoo! answers type of site now.  

Witcoin was the first community site to integrate bitcoin.  It was such as small community then and the site ended up closing.   Ogrr.com probably does the best job of this today.  But there are other examples -- Rugatu, and in many ways, the signatures here on the BitcoinTalk forum are frequently used for this since the forum software itself doesn't support associating a bitcoin address to a profile yet.  It does display the URI handler though.  So if I show a bitcoin address here, such as the Faucet's: bitcoin:15ArtCgi3wmpQAAfYx4riaFmo4prJA4VsK it gets formatted nicely for use by your URI-enabled client.