Clever ways to determine which containers/bobfiles to build

[rafecolton]

For example, "I'd like to build all containers specified in each Bobfile that lives in a directory in which at least one file was changed in the most recent git commit."

I'd like to use this thread to brainstorm different use cases, described as above - in plain English. They don't have to be git-related, though I think that is an area with a lot of opportunity.

Then, after we've brainstormed for a while, let's implement!