Preview at WWDC likely in June, followed by September launch.
Thunderbolt Coming to PCs in April 2012
Intel and Apple originally partnered on the new technology which has become standard across Apple's MacBook Pro, MacBook Air, Mac mini, and iMac. Digitimes reports that the cost of Thunderbolt technology is expected to drop in the second half of 2012, allowing more widespread adoption.
While Apple does offer Thunderbolt across most of its product line, the first Thunderbolt products have been limited to relatively high end devices. More widespread adoption should help drive adoption by accessory makers that will benefit both Mac and PC users that use Thunderbolt.
Intel has always said that they see both USB 3.0 and Thunderbolt as complementary technologies and plans to support both in their 2012 motherboards.