A very cool usecase!

"Have a weird build failure like a segmentation fault in the compiler? Publish the Docker image and have someone take a look! No need to take the builder offline while someone SSH's into it. "

In particular this notion of using it for a build environment, and then being able to share the EXACT problem with the build with other developers strikes me as a very interesting. I can imagine many build environments to benefit from such. Any failed build (in automation) can be handed to you as a chocolate on a platter.

Since people continue to post about docker without much news or comment on usage. Here is a real thing being used to build Firefox.