I reckon theres a good bit of money in it, they do it in my mums area (in london) Its a terraced road, and one will drive down the road slowly while the other two hook the bins on the back, it only takes about a minute to clean two bins at a time, and whilst one guy returns them to the gardens the other is hooking on another two.
They have a customer every three or four houses so there machine is constantly working, at £2.50 a bin they must take £100 just of that road, and there only there 15minutes.
They do this all morning, you do the math.
Biggest problem must be taking the money, as my mums often 2-3 months behind, as shes not allways about when they turn up.