I was considering this for a website I worked on, but the license agreement for RecipeML put me off:
Mention that your site/software uses RecipeML by name. (If it is software, you need to get permission first.)
Not that it's all that restrictive, but sheesh, it's a markup language. The value comes from having as many people use it as possible. The license makes me suspect they're trying to make a buck somehow, which I view as putting the brakes on making it ubiquitous.
This site powered by HTML!
For folks on a diet, lowcarbcooking.org is a good resource, with recipes in many different categories.
(disclaimer: I helped build the site)