You should by Time Machine. Hope that helps.
You need to use the same iCloud account.
Use the keychain of your Mac to recover it.
if you have issue on creating Cloud Memo on Mountain Lion please update to version 10.8.2
They are not lost and will be recoverded on the next update.
a fix is coming.
They will be shown after the update.
iCloud on Mountain Lion is not working, an updated version is already in approval to Apple.
You can fin them on your old preferences.