(Also Matt 22:30 and Luke 20:35)
In context, the Saducees, who are more interested in Temple sacrifice as a means of ensuring well-being in this life than interpreting the law of Moses to make sure you make it in to the next one, are trying to trip Jesus up with a catch-22 in the law. Essentially, the "Law of Moses" says that if a widow is left childless by her husband's death and there is an unmarried brother-in-law available, she and the brother-in-law are to marry. The Saducees concoct a hypothetical situation where there are seven such brothers, and each takes a turn marrying the woman and dying without offspring. The Saducees ask Jesus whose wife she'll be in the afterlife (presumably either the first or the last brother to marry her I guess, but you can see how they thought they had him good.) Jesus first insults them, asking more or less "Don't you know the law and the prophets or the power of God or [and I'm guessing here] are you just stupid?" He then ruins the plans of couples who plan to spend eternity together.
This is probably why the unpleasant "...'til Death do you part" corollary is inserted into the otherwise joyous wedding vows of most christian couples.
Nonetheless, this is more evidence that Jesus wasn't a big proponent of marriage. Neither was Paul in 1 Corrinthians. You don't hear this passage a lot from the American Family Association types, or from anyone whose financial well-being is based on the idea of familial regeneration to populate an organization from century to century. I guess you can't blame them for decontextualizing the Bible so often.