"That already exists," she said, "My sister uses it!" She called her sister and found out the application is called Gourmet Recipe Manager. Although it is designed to run on GNOME, their site claims it should run on Mac OS X and Windows as well. (Apparently there is a Windows application called MealMaster/Cookbook Wizard that is similar.)
Although it currently tries to guess where you might find celery ("produce") to compile your shopping lists, you can create your own categories so that celery might appear on my shopping list under "farmer's market." The only thing it lacks that my dream application had is the ability to identify ingredients by season, so that I could easily sort through a list of winter recipes. Perhaps I'll add that suggestion to the feature request page.
And, indeed, the recipe export options include XML, so you can easily send recipes to your friends. Well, your friends that use Gourmet Recipe Manager. Everyone else will have to live with plain text or a PDF.
If you are interested in cooking and computers, give it a try! I'm itching to trade some XML with y'all.
x-posted to ungodlikediet