Can you offer some resources on spinning Boucle?

Aha. So the recent ever-so-brief explanation was not enough for you, I can understand that completely!

There are great explanations with pictures in the books

Essentials of Yarn Design by Mabel Ross

and

Spinning Designer Yarn by Diane Varney

I know it takes mohair or ingeo or a few other fibers to get the loops to loop correctly. I expect it may have something to do with the crimps per inch of the fiber -- if I had to guess, I'd say look for a fiber with not more than 3 crimps per inch. The drawing shows you what I mean about crimp length, as opposed to fiber, or staple length... (picture © 2006 The Bellwether, from Spindling: The Basics, used with permission.)

Here's a discussion page I found with a similarly brief description of boucle, but with a ton of additional feedback and further explanation that really helps explain things:

http://www.knittersreview.com/forum/topic.asp?TOPIC_ID=49689&SearchTerms=,boucle

They point out there that the Winter 2005 Spin-Off has an article on novelty yarns, including boucles, by Judith Mackenzie-McCuin.

And if you are anywhere near Puyallup WA, on April 20th, 2007, then I can heartily recommend that you sign up for the class "Boucle Without Tears" by Diane Bentley-Baker at the Shepherd's Extravaganza. She's a terrific teacher and funny to boot!

(this posting inspired by recent questions on spindlers and SpinningOnTheEdge)