Intel originally planned to launch the chip in 2008. Multiple delays forced them to push those plans until "sometime in 2010," but apparently the company has fallen behind where it hoped to be in silicon and software development at this point, and don't believe their product would be suitably competitive with Nvidia and AMD's alternatives by the time of release. The idea behind Larrabee was to offer graphics and parallel processing with the full programmability of an x86 CPU, using a many-core architecture based on the original Pentium design.
The announcement came as a bit of a surprise considering the company had been working on the project for the last two and a half years. It also showed off a system based on Larrabee just three months ago at IDF.