Normally, I don't need to do much maintenance but I tried the following:
- Booted from my install DVD and ran disk utility (that did fix some problems including a file I couldn't previously delete)
- Running Utilities/Keychain Access and getting it to repair my keychain (it found nothing wrong)
- Deleted keys with Keychain Access that were used by apps that gave me trouble.
- sudo mv /var/db/CodeEquivalenceDatabase /var/db/CodeEquivalenceDatabase.old
And all is well.
Reading around, it seems this is a rare but repeated problem.