Chip,

Just my opinion, but I like split-thread technique better; one less tool to grope for (hook, twister, whatever) - the bobbin does all of the work (beefy ones like S&Ms work great). Just make sure to use the right thread - bonded ones like Uni 6/0 or 8/0 don't work well. Here's some pics:

http://www.pechetruite.com/Mouches/cdc-dubbing2.htm
http://www.pechetruite.com/Mouches/caddis_e.htm

This is also a great way to re-enforce aftershaft feathers if your using them for something like the head on a Casual Dress.

Regards,
Scott