Well, I wouldn't bother logging a taxi that didn't involve a flight either (one 10-minute 'drive' requested by a friend because it was too windy to fly but she wanted to at least be in an aeroplane with me springs to mind). However, I was taught to log brakes on - brakes off.
And I have to say, to me this makes sense. You're not actually flying during the taxi, but there's no doubt that you're needing some of the skills you would need if you were.
For example:
*R/T (in many cases more intense on the ground)
*keeping an eye on your engine and performing the pre-flight checks
*being responsible for the well-being of any pax
*getting yourself mentally organised
*being in the right place at the right time - not taxi-ing into anything (_much_ more of a danger at night, which is why you'd be daft to try it without the rating, IMO).
Some of this is probably more pertinent at a larger aerodrome with ATC service, but I still think it applies anywhere.
So while it doesn't matter that much to me and I've not been deliberately logging a few more minutes out of desperation for hours, I'm not about to go back and re-calculate my whole log book.
So there.
