Ok - now I'm doing this by memory as I have loaned out that copy of that book - but I THINK it's on page 39 of "Timber Frame-Home : Design, Construction, Finishing" (not 'Timberframe : The Art and Craft of the Post-And-Beam Home' which is basically a photo-essay of the beauty of timber frames)

In any case, it's easily located in the index - you have to hunt around on the page for it - but he mentions the 1/2 figure.

He also notes, much to my amusement, that since the engineering fomulae for knee-braces really don't exist, he designs his frames to be stable _without_ them, and then adds the knee braces as extra contingency stability.

Which I found to be encouraging, as it meant there might be a way to elimate the suckers after all!

Also - if you check out the website for Cascade Joinery, you'll see a lot of double girts in their photos and a lack of knee braces around those trusses.

STILL - if there are any knowledable designers/engineers/builders who have a comment on this matter, I'd much apprciate it.