Simple organization of recipes. iTunes/iPhoto kind of organization. Allows user defined categories and sub-categories. Searchable.
In-place editing. Some software have a presentation view that is different from a editing view. That's cumbersome. Measuring Cup edits recipes as easy as when you are viewing it.
Undo/Redo support. Good - no, make that great - undo/redo support.
Simple view of a recipe. Shows the most important detail in the main screen. The rest is tucked away in an Aqua drawer.
Sharing of recipes via import/export
XML backing store. You probably don't care about this but this is cool to mention it. All recipes are stored as XML file for easy sharing eventually.