Another shameless plug? possibly... but apropos.
Great suggestions thus far, so in the spirit of TIMTOWTDI I would suggest having a look at
The Uniqueness of hashes.
It's a collection of some techniques for just this sort of operation.

-InjunJoel
"I do not feel obliged to believe that the same God who endowed us with sense, reason and intellect has intended us to forego their use." -Galileo

In reply to Re: What is the best way to get just the duplicates from an array? by injunjoel
in thread What is the best way to get just the duplicates from an array? by wenD

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