Empty iCloud Drive folder in Yosemite? In OS X Yosemite, my "iCloud Drive" folder is always empty.

My Macbook is running Yosemite, and my iPhone and iPad are running iOS8. I have gone through the iCloud Drive migration process and it does work on my iOS devices - along with iCloud.com.

I tried turning iCloud Drive off and on, but that doesn't fix it. Nor does completely signing out of iCloud and signing back in. (With reboots in between every step)

Short of a re-install, is there anything else I might be able to try to get my iCloud Drive in working order?

Thanks.
Do you run firewall software?  If you do, check if you're blocking calls from
the nsurlsessiond to the amazonaws.com domain.