Bruce Schneier has a blog post that talks about trashcan usability in terms of finding the right balance between security and ease of use: Human/Bear Security Trade-Off
From the blog post, ending with one of the best quotes ever:
Back in the 1980s, Yosemite National Park was having a serious problem with bears: They would wander into campgrounds and break into the garbage bins. This put both bears and people at risk. So the Park Service started installing armored garbage cans that were tricky to open — you had to swing a latch, align two bits of handle, that sort of thing. But it turns out it’s actually quite tricky to get the design of these cans just right. Make it too complex and people can’t get them open to put away their garbage in the first place. Said one park ranger, “There is considerable overlap between the intelligence of the smartest bears and the dumbest tourists.”
Take a look at the comments on the post where all manner of clever and cynical comments add to the post.