iSync shows no computers registered (!), can’t add computer

Turns out the fix is simple.  Apple tech support told John “OK, issues (in Mail, Keychain Access, and MobileMe) seem to have been resolved ultimately by a reboot and unregistering and re-registering computer in MobileMe. Apple support called me back in less than a minute, were knowledgeable and efficient. (But I guess we’ve come to expect that, don’t we?)”