Mountain Lion is nice, but by default it wants to save things to iCloud – and if like me you create and save loads of documents every day that you want to store locally, that gets very annoying very quickly. Here’s how to change it so the default is your Mac’s hard disk:
Open Applications > Utilities > Terminal
Paste this: defaults write NSGlobalDomain NSDocumentSaveNewDocumentsToCloud -bool false
Hit enter, logout and log back in again.
And that’s it. You can undo the change by pasting the same thing but with “true” instead of “false”.