Following up on Jpatokal's answer. After staying for a month or so in Bali, I got stopped two times by a police control.
Each time they asked for a bribe of 200'000 IDR to let me go. The first time I only had 100'000 IDR in my wallet, they ended up accepting it. The second time I was ready with a dedicated pocket having only 50'000 IDR, and they ended up taking it. Note that each time I told them I had not the 200k the policemen were not amused, so I had to put on a act so they believed me and ended up giving up.
Where the police stopped me
The first time, two cops stopped me on this epic bridge linking Sanur to the Bukit peninsula, at the toll where you pay for the fee to take the bridge, it was exactly here
There is a dedicated queue for motorbikes at the toll. And behind was 2 policemen stopping motorbikes one after another, they were doing a killing. I stopped only a few minutes and I saw them getting bribes from 2 other motorbike riders, a local and a tourist.
This is the policeman stopping motorbikes just after the toll.
This is the other policeman taking the bribe in his booth while the other one stops more motorbikes
The second time, a group of around 15 policemen were located on a main road just after a curve (close to Kuta), stopping many motorbikes, and again, stacking on illegal money from bribes.
I think it was here exactly, http://goo.gl/maps/DMQsF