Followup note (8.28.07): I traced the problem back to Safari. I recorded the second session using Firefox, and was able to record and save the video just fine. So, use Firefox when you’re using uStream on OS X.
A shorter note: When saving a recording, make sure – 100% sure – that the recorder window prompts you to do something. Like ‘save’.
I just finished up and closed the recorder. Apparently, something in my browser went wonky, didn’t display the save dialog (I think) and my recording is gone. Poof.
It’s not a total loss – the video producers here recorded everything, too. But avoid the heartbreak of broken links and lots of people e-mailing you. Don’t close the window until you see the save dialog.