The local Post Office just installed a new self service machine for mailing large packages. I was at the front of a short line when an office manager approached the older couple waiting behind me and asked if they'd like to use the new self service machine in the lobby. No, they hadn't seen it. No, they wouldn't like to try, they had to pay with a credit card. "It takes credit cards," said the manager. No, they didn't like using machines that took credit cards. The manager exhorted them for a little while longer, then gave up and left.
The manager needed to pick his spots a little more carefully. Everything was working against him at that particular time. All customers who walked in could see that the line was short. A couple of regulars were working their stations, and things were moving along pretty smoothly. The couple could see that they wouldn't have to wait long, and weren't anxious to leave the queue to wrestle with a new device. "New self service machine" doesn't exactly inspire confidence in anyone.
Maybe the biggest disincentive for self service in the post office is that it prevents you from talking to a real person. I attended a talk many years ago on why older consumers wouldn't use ATMs. After working hard for a while on the machines' usability problems, older consumers still refused to use them. The presenter conducted some interviews and discovered, not too surprisingly, that many older consumers simply liked to talk to the bank clerks. They were retired, they had time on their hands, and they liked to talk to people. No amount of usable design was going to overcome that issue.
Companies trying to increase the usage of their self service IVRs during regular office hours face similar issues. Customers already have had experience with a lot of misbehaving IVRs before they reach yours, so there's a tendency to be a little skeptical. If the queues are short, and people know they're short, they'll opt to talk to a CSR. It's fast and easy, and a lot of customers just like to talk to people. After hours, it's a different story. Customers may take a shot at self service to avoid calling back the next day.
If the lines at the Post Office are long, people will be motivated to try the self service machine. As I left, I noticed a problem that will discourage adoption. The machine had been built flush against a wall next to the commonly used mail slots. There was no way to logically form a queue for the machine without standing in the most heavily trafficked area of the lobby. The Post Office will need to learn the lesson that the airlines needed to learn: you have to design a queue for self service, too.