As an employee of Uncle Sam himself, I'll offer an opinion on this. I see people working hard every day. I myself probably worked 55 hours last week and maybe 50 the week before. Those were for a particular problem so I got comp time for them, but just as often a big thing comes up on short notice and I'll work late to get it done. No biggie - it happens. I see the same thing from my co-workers and the contractors in the office work right along side us.
The misconception, I think, is that we often see unmotivated or unresponsive people at places like the DMV or (in my case) at the Army Frequency Allocation office.
We assume that they're lazy because they're not afraid of being fired since they're civil servants, when in fact they'd probably just be just as lazy working in private industry. They might move jobs more often when they're upset about not getting raises, but it doesn't seem like many people are dismissed in private industry unless they're doing a really bad job, or if the company is in trouble. In gov't work, instead of being fired, often people are pigeonholed into some lonely menial job. They might get paid well, but they'll HATE it. Some of them quit. It's not quite being fired, but the upshot is the same.