Toyota offering $750 in dealer cash on 2009 Prius

That might work in southern California but it would be absolutely no incentive for the majority of America. In the 15 years I've been driving I've lived in a city with a HOV lane for exactly six months. That was the Hampton Roads area of Virginia. When I lived in Tennessee the closest HOV lane was 4 hours away in Nashville. The state of Michigan has exactly one HOV, Michigan Ave in downtown Detroit.

You also have the problem of saturation. Eventually the HOV lane will be just as slow as the regular lanes as they fill up with hybrids. Personally, I think HOV lanes should be reserved for their original purpose, car-pooling.