Fun but a bit big for such usage, you have the Drifter Scooter (http://www.pulsescooters.com ). In a similar vein, you have the Flash Wheel to have wheels on any shoes you wear (instead of having shoes with wheels in the heels -- http://streetgliders.co.uk/ ), the Spooner to surf anywhere (kind of skateboard without wheels-- http://spoonerboards.com ), the Magic Wheel (a scooter with only one, big wheel-- http://www.amazon.com/Magicwheel-MW1-The-Scooter-Skateboard/dp/B0013K0MKY ) or even the good old monocycle seen in circus. Alas, most of them need for training/good sense of equilibrium, but they are fun to use and can be easily taken with you, as you point out (no need to anchor them outside).

"spoken communication puts a highly disproportionate burden on the listener." I fully agree! What is funny is that you mention podcast later... Personally, I avoid these numerous and surprisingly popular video tutorials or podcasts, partly because I am much better at reading written English than at understanding spoken English (depending on accent, too), because I am French. And mostly because most of the video tutorials I saw are excruciatingly sloooow, we wait for the cursor to slowly move and hesitate to a menu, move elsewhere, etc. And I don't have sound at work anyway. It is much faster to read a tutorial on a Web page, to print it out to read on the public transport, to skip some parts I already know, etc. I understand the interest of video in some fields (eg. a demonstration of a manipulation in an image editor), much less in other fields (typing code in an IDE!). But perhaps I am too old fashioned... :-)