Hmmm... are you supposed to rate 5-stars for acceptable service? I've been rating 3 by default - then plus or minus depending on extraordinary things.
Quoting from http://www.youtube.com/watch?feature=player_detailpage&v=C4r...:
"Engineers do not give out 5s. If you tell an engineer that the possible rating scale is 1 to 5 and they like you, they give you a 4. Because tomorrow they might love you and then they would give you a 5. They probably won't, but they might, so they give you a 4 so that they have room. We all are totally okay with this. But the world is also full of this other class of people who if they like you give you a 5. They're quite consistent about it. 'I like you. I see nothing wrong with that. I'm giving you a 5.'"
The graph (with, admittedly, artificial data meant to portray an example) at http://www.youtube.com/watch?feature=player_detailpage&v=C4r... shows it most clearly, with the satisfaction numbers from engineering clearly trending down. Apparently, engineers don't like to fill out forms, while admins do, so satisfaction survey results also have a sample bias in favor of the 5s of admin staff.
You accidentally rating someone 3 for an average service can actually cost them their job. I'm hoping their algorithm uses some sort of a weighted average to offset the ratings of individuals such as yourself who consistently rate very low.
i.e. If I always rate 3, but sometimes rate 1; then that might be similar to someone always rating 5 but sometimes rating 1-3.
Ah, but then a user might throw an Internet Fit(tm) and cause a public outcry about ratings being manipulated by Uber etc. etc.
There are a lot of ways in which a ride can be unsatisfactory (smelly, creepy, crappy car, poor driving, loud music, etc.) but not that many in which it can be exceptional. Unless they show up in a Tesla Roadster or something.