Sources within the graphics industry expect to see Larrabee retail products in late 2009 and currently neither Nvidia nor ATI sees it as a threat, at least not in a short term.
Intel promised to show Larrabee in late 2008, but everyone who has been in this industry a few years knows that Intel has to go through painful driver development and polishing cycles.
It took ATI years to catch up to Nvidia on the game support and drivers and Intel's IGP driver is simply a laughable application that shows a 2D picture and plays some video.
Until the later part of 2009, Nvidia and ATI will be the only two GPU manufactures to consider and even when Larrabee launches you shouldn’t expect a miracle, at least not from the first batch.
I’ve heard once that in semiconductor industry start-ups you earn the money from a second chip, not the first one, and this will shed some light on some of Larrabee’s expectations.
However, the same sources believe that long-term Larrabee and Intel’s future GPUs will become a serious threat, but it will take time, especially for the driver part of the story.