A new study by Mercury Research found that AMD saw big marketshare gains in Q1 2010, at the expense of NVIDIA:
AMD's graphics business gained 8.2 share points in the discrete market, for a total 42.1 percent share in Q1. As you might have guessed, Nvidia lost 8.2 share points over said quarter. In mobile graphics, AMD gained 9 percent and ended up with a 49.7 percent share.
In overall graphics sales, including the integrated GPU market which is dominated by Intel, AMD gained 2.8 percent. Nvidia dipped 4.8 percent and it can only hope that sales will pick up with the introduction of new DirectX 11 parts.