For me, the upper limit of acceptable commute time is 10 minutes, but a longer commute time does give me time to think up of things while navigating a familiar route. One such idea came from a sudden desire to write a book. Having gotten Stanza for my iPod, and having a mind that cross-links ideas together like an encyclopedia, I'd want to publish it via epub and on a MediaWiki platform. I'm getting too old for copy-and-paste editing, so having a source document written in ERB would be ideal. In fact, I even got as far as a vague notion of using Nokogiri and/or XML as some sort of intermediate representation.
Turns out, while (as usual) searching for something completely unrelated, I found that someone has already implemented this tool: http://snk.tuxfamily.org/lib/erbook/.