Thanks to Michel for the information:
It is now official, directly from Apple:
Today we are announcing the availability of the NVIDIA GeForce 8800 GT graphics card kit for the 1st Generation Mac Pro expanding the range of graphic cards available. Please note this kit is different to kit for the current generation Mac Pro's. We are also today introducing aggressive new pricing for the ATI Radeon HD 2600 XT Card and the NVIDIA GeForce 8800 GT bringing the price down to 100 and 230 respectively.
So only good news! Interesting to see how Apple seems to reconsider how graphic card upgrading might be beneficial for Mac users or maybe this is to prepare the introduction of the Radeon HD 3870 as we recently spotted it in a TechNote from Apple
Beside the announcement, the