We've seen mouse sensors based on one laser,
According to the Razer press release, the 4G Dual Sensor System "lets you determine the cutoff height for tracking to stop when the mouse is lifted from the surface. This is especially important for gamers who pick up their mice to accommodate wide swiping motions." In addition to height detection, Razer also attributes to its sensor design a new 6,400dpi tracking sensitivity.
The 4G Dual Sensor System will come to market via updated versions of Razer's $130 Mamba and $80 Imperator gaming mice this month from Razer's Web site, with worldwide availability slated for July.