Update: whoops, I originally posted this calling it VB 5, but was contacted by Qarbon who pointed out it's actually version 4 (they're still working on 5 for the Mac)
Well hot on the heels of my complaint about not having a tool to edit .mov files, Qarbon shared with me a beta of ViewletBuilder 4 for the Mac. Now, they've had a Mac version out for some time, but also for some time the version they had didn't support sound. They appear to have that bug licked.
While I'm no longer a huge fan of the ViewletBuilder / Captivate model of taking individual screen shots and then animating them after the fact, I do certainly appreciate the ability to mark up the screencast. Here's a long (15 minutes!) walk through of how to build and annotate a very basic screencast using ViewletBuilder 5 on the Mac. If you want to actually see what's on the screen, look for the full screen button in the upper right.
Qarbon offers free hosting for two Viewlets of any size. Educational pricing for ViewletBuilder is $199.
You can watch the actual Viewlet I built here. (there doesn't appear to be a way to embed)