A forthcoming study on online dating from the Journal of Evolution and Human Behavior finds that few participants share their political beliefs with potential dates:
Even among the subset of people that were willing to explicitly state their political preference on their dating profile, the vast majority (57%) stated that their political belief is "middle of the road". … So among the roughly 50% of users who were willing to state a political belief, a very small number were willing to actually be definitive about what that belief was.
The Dish 