They are increasingly common:
American rates of inter-faith and inter-denominational marriage are rising, to the point where 45% of marriages in the past decade have involved either two religions or Christian doctrines that clash seriously (that rate includes unions spanning the evangelical and mainstream Protestant traditions—when all Protestants are lumped together, the mixed-marriage rate is 36%). Many are models of tolerance and creativity. Naomi Schaefer Riley, author of a new study of such marriages, records a wedding which featured two New Testament readings, the breaking of a glass (recalling the first-century destruction of the Temple in Jerusalem), the reading of a Jewish marriage contract, a transcendentalist poem and an Apache wedding prayer.
But there are some downsides to this development:
Inter-faith marriages are more likely to end in divorce. Half of marriages between evangelical Protestants and non-evangelicals fail, and prominent evangelical pastors warn of the “emotional anguish” of marriage to someone who does not share their strict interpretation of faith.
The Dish 