Going back to a couple of subtopics mentioned briefly earlier:

Yodeling: Does it seem to you (as it does to me) that this sound is produced by shifting quickly back and forth from "normal" to falsetto and back, i.e., in and out of falsetto?

Females doing falsetto: I had never had the slightest inkling that falsetto was a male-only preserve, and was a bit surprised to read those posts that expressed doubts that women could/would use this technique. I don't know about Nelly F. mentioned above -- since I live in New Orleans, a town with its own musical culture, I'm able to completely ignore mass-media pop -- but I can offer Lucinda Williams as another example of a falsetto-singing woman. She definitely writes falsetto-high notes (and yodelesque transitions to and from those notes) into many of her songs. Now, she's by no means a soprano, more of a deep alto -- maybe it's the true sopranos who can't do falsetto, because their regular voices get them up as high as anyone can sing (or maybe even hear)!