Saved here for posterity:
To get your data into the OPVault format, you need to follow one of the following sets of instructions, depending on which version of 1Password you're running: Windows (version 4), Mac (version 5) from our AgileBits online store, or Mac (version 5) from the Mac App Store.
Note: It is not possible to reliably create OPVault in earlier versions of 1Password for Mac.
Caution: 1PIF is a plain-text format, so your data IS NOT encrypted. Be sure to delete the 1PIF file securely!
In 1Password for Windows:
When finished, please securely delete the Export-Delete-Soon folder in your Documents\1Password directory.
Note: It is not possible to reliably create OPVault in earlier (pre-5) versions of 1Password for Mac.
If you're on the beta track of 1Password 5 for Mac from our online store…
Disable sync, if it's enabled, making sure you enable the Delete data option.
In 1Password 5 for Mac (beta), choose Help > Tools > Enable OPvault for Dropbox and Folder sync.
Re-enable sync, making sure you don't select an existing .agilekeychain or .opvault folder as the sync point.
If you're not on the beta track, or if you're using 1Password 5 for Mac from the Mac App Store…
Caution: Terminal commands are a very powerful tool with which you can unintentionally render your Mac's operating system unusable. If you choose to use the command, it might be safer to copy and paste it than to type it by hand.
In 1Password 5 for Mac, press Control-Command-Q.
Launch the Terminal app, and issue the appropriate command:
If you obtained 1Password 5 for Mac from the Mac App Store…
defaults write 2BUA8C4S2C.com.agilebits.onepassword-osx-helper useOPVaultFormatByDefault true
If you obtained 1Password 5 for Mac from the AgileBits online store…
defaults write 2BUA8C4S2C.com.agilebits.onepassword4-helper useOPVaultFormatByDefault true
In 1Password 5 for Mac preferences, disable and then re-enable sync.