Firefox 3 Download Day Mega Widget
Update: Oh, and rumor has it that this widget will switch to reporting on downloads, rather than pledges, once the main event has begun.
Update 2: It didn't quite go like clockwork, but this widget is now showing estimated downloads by countries, rather than pledges.
Thanks to the completion of bug 435967, I can offer this totally unofficial hack of a mega widget (better late than never):
If you'd like, you can include this on your own site with a Copy-and-Paste of the following: