Seattle Tries Large Scale Real-Time Ridesharing Pilot

It’s called Avego and is state-funded:

The pilot program allows 250 drivers with GPS-enabled smartphones to offer the empty seats in their vehicles to 750 riders along the SR 520 highway, in real time, as they travel. Avego pairs passengers and drivers through a system using iPhones and other mobile devices.
...
To encourage participation, Avego will reward go520 drivers with a $30 gas card monthly, plus travel reimbursements, for participating in the program 20 or more times each month. Drivers will also receive an Avego iPhone accessory pack (retail value $35). Riders will receive up to $30 per month in Avego credit to use towards real-time ridesharing journeys. In addition to these financial benefits, drivers and riders will be able to reduce commuting time by making use of the high occupancy vehicle (HOV) ramps and lanes.