I just noticed – Google has added a recipe search item to their home page. You can filter the results by ingredients, cooking time or by calories.
To get included in the results, sites need to tag their recipes using rich snippets.
Rich snippets can also be used to add information (e.g. geo-location, address, phone number) that Google uses in its search results for other types of data about (for example) events, product reviews, or businesses. It looks like it would be a good idea for businesses to add the necessary code to their sites and then tell Google that they have done so.