I tweeted about this the other day, but thought I'd upload some pictures too. The other day I was seated in a bulkhead seat and wanted to consolidate bags (I was carrying my Imago, Western Flyer, Side Effect, and Field Journal Notebook). I was able to stuff the Side Effect in the front compartment of the Western Flyer (along with shoes and a packing cube with some clothing), and the FJN fit nicely in the rollerboard pocket on the back. I was then able to put the WF and Imago upright in the overhead.
One of the things I like about the WF is how structured it is. It stands upright, even when unzipped, making it easy to rearrange things in the airport.