This tip comes courtesy of JC at Mac Geekery, who has discovered how easy it is to roll your own QuickPicks for .Mac Backup by editing the DefinitionPlist.strings found inside the packages within Library/Application Support/Backup/QuickPicks/. QuickPicks are those pre-defined backup sets that grab specific types of essential files, like all your Excel docs, or your entire iPhoto or iTunes Library, or all your text files.
As JC points out, many 3rd party apps install convenient QuickPicks of their own, but for those that don't, you can now create them yourself without breaking a sweat. It's little things like this that you don't realize just how handy they are until someone else points it out. And remember, kids... you're only as good as your last backup.