I tried unplugging the hub. It didn't make a difference.

I unplugged the wireless USB transmitter for the mouse from the Mac and plugged in a corded USB mouse (another Logitech). It still hangs, but it's much less frequent using the corded mouse. (Plugging it in directly or via the hub didn't seem to matter.) That tells me that it may be a mouse driver or mouse brand issue.

Perhaps this is Apple's way of telling me to buy a Genuine Apple mouse... ;-)

Oh well.

Thanks again.

Cheers,
Scott.