Well, many folks on "Apple's discussion":http://discussions.apple.com/thread.jspa?messageID=7026416 are talking about performance issues with 7.3.1. Like me, I now lose the connection to the Time Capsule drive and then Time Machine fails and looks for a password (which should be on the key chain).
The other problem is slow network "speeds":http://discussions.apple.com/thread.jspa?threadID=1477962&amp;tstart=-2 where folks are seeeing speed stuck at 2Mbps (I see 2MBps), but when they go back to 7.3, they get back to high speeds. That is what most folks are seeing. 2MBps even on large copies. Also, the MacBook Air looks stuck at about 2MBps writing while the MacBook Pro is at 9MBps as "Macintouch":http://www.macintouch.com/reviews/timecapsule/ reports. As an aside, you should get about 14MBps with a direct gigabit ethernet connect.
Here is how you downgrade:
# Start /Utilities/Airport Utility
# Click on your Airport and click on Manual Setup
# Choose Base Station/Upload Firmware and you should see 7.3.1 and 7.3