Another *possible* problem w/new firmware?
I just upgraded both my Airport Extreme (latest revision) and Airport Express (latest model too) with this 7.63 firmware and all seemed to be well initially.
A few hours later, my wife tried to kick off a Time Machine backup over the LAN to my FreeNAS box serving as the makeshift Time Machine server (always worked pretty good before), and the backup suddenly halted.
I went downstairs to troubleshoot and realized the Airport Express and the Extreme which I had been running in bridged mode, with the Express extending the wi-fi network were not seeing each other. Both still had green lights on the front, but no network traffic was flowing between them at all.
I rebooted the extreme by unplugging the AC power, and when it came back up, all was well again. But now i'll have to keep an eye on it for a while to see if this was a one-time glitch, or a problem with the firmware.