Anthony Rickey comes out in favor of dating across party lines. It's a fine thing to do and sometimes an impassioned and exhilarating discussion between opposites is rather sexy in itself.
However, I think Mr. Rickey underestimates the difficulties of such relationships. Being with someone with whom you disagree on fundamental issues puts obstacles in the path of the relationship that need not be there, and other people are difficult enough. I venture to say that most of the people on Act for Love don't just think that Republicans are wrong, but that they are bad: a morally deluded or intentionally wicked force for evil. It's hard to date someone you think is attempting to destroy the country. If you are looking for a long term relationship, then the issues multiply and take on greater weight.
If you seek mere bed partners, a willingness to date your opposite political number may broaden your pool of potential dates and open you up to a heady clash of opinions. However, for those of us who are in search of a life partner, it may be wiser to choose someone who will support you in your ambitions and aid you in your endeavors without feeling he is betraying his dearly held principles.
On a side note, I am not sure defining tolerance as the ability to separate feelings about a person from feelings about their ideas is good. Other than your essential humanity that makes you worthy of individual respect, your personality is largely defined by your actions and beliefs. If a very sweet and intelligent person holds morally repugnant beliefs, I think they should be held accountable for those beliefs instead of given a pass because they are "nice." Of course, not everyone ties goodness to acceptance of proper philosophical positions as I do.
Edited to add that I am thinking particularly of dating activists; there is a sharp demarcation between dating someone who simply subscribes to different beliefs and someone whose identity and existence revolve around changing the world to bring it in line with those beliefs (Amanda Butler outlines the distinction nicely here). Such behavior repeatedly remphasizes the conflict in the relationship and puts the disagreeing parties in more uncomfortable situations. If I ask a Democratic boyfriend to come to the Christmas party at a heavily Republican firm, that is a whole other kettle of fish from asking him to accompany me to a pro-war protest, say. There is the pleasant frisson of "dangerous belief" and there is the cold and annoying reality of having to sanction or support causes you find highly objectionable to satisfy the emotional needs of an activist significant other.