I suppose this was to be expected really with the huge success of the ATI 4 and 5 series.

Days after Apple announced that the new iMacs and Mac Pros will switch to AMD's ATI graphic chips, a second quarter marketing report has revealed that the company has passed their rival NVIDIA in total shipments.

According to CNET, Advanced Micro Devices (AMD) now holds a 51% share of the standalone or "discrete" graphics processor market, with NVIDIA's stake at 49%. This is a significant change from last year when NVIDIA controlled 59% and AMD trailed with just under a 41% share. - source
I wasn't aware of this though:

AMD and NVIDIA both play large roles in the gaming sector with Nintendo and Microsoft using ATI chips for their consoles and Sony working with NVIDIA for the graphics processor on the PS3.
This should really be taken with a pinch of salt, but it's nice to see the competition hotting up a bit.