I've noticed a few cities dropping rates after getting in the door with drivers - it makes it so that it's not as worth it for drivers. There's also not a ton of control of how many drivers are working a given area, so you could wind up with too many for the demand and have a hard time getting fares.
Overall, I love Uber, but I've been screwed once. In Chicago, late at night getting picked up from the bus station. Called an uber, on the way at 1.0x pricing. He cancels 2 minutes later, another on the way at 1.4x then cancels, followed by a third at 1.8x - it was pretty shiesty to see my price jump that much just because the drivers knew they could get more demand for different fares. But hey, still cheaper than a cab.