Exit Poll Failure

Pundits are saying the exit polls mistakenly gave the edge to Kerry, and were also problematic in the 2002 election. In theory they should work, because there is not much reason for someone who just voted and is asked to identify their vote unanimously to lie. But if they don't work that well, then what is the use of having them, rather than just waiting a little longer for the results to come in from the election officials? Maybe they will become a thing of the past.