Okay, I think I can definitely say that uvcvideo, and weblook, freezes when ACPI switches off all but one processor.
One odd thing, that I see, is that starting weblook causes some low activity on the second processor, even though the system does not appear to have enough activity to justify turning it on.
When I also start webview, the activity does go high enough to turn on the second processor, and keep it on (depending on the settings).
I don't know if this is a flaw in ACPI, the USB stuff, WebSee, or something else.