Do you have a Mac Pro purchased sometime between August 2006 and January 2008? Have you been seeing distorted video and unsightly video artifacts? If so, Apple has created a special repair program for you. Under the terms of the program, you can take your old video card (along with your Mac Pro's serial number) to an or an  and exchange it for a new card.
Video cards that are eligible for exchange under the program have the characters "V6Z" in the last part of the card's serial number. In order to verify the card's serial number, you will need to open your Mac Pro and remove the card; you can't see the serial number when the card is installed. Apple has published a support note, "," that explains how to remove the card and verify the serial number. The support note also points out that you do not need to exchange the card if it does not exhibit signs of distorted video.
The exchange program, according to Apple, applies to "affected ATI X1900 XT video cards three years from the original date of purchase or until January 31, 2011, whichever provides longer coverage," although Apple may extend the program if necessary.
If you have already paid for a repair or purchased a replacement video card, you may be eligible for a refund; contact Apple for details.