I've just discovered this site and I love it, so I thought I'd share it.
I have a silly amount of cookbooks and often start with the ingredient or idea rather than with a recipe. (I might find I have a pile of courgettes left over in the fridge, or I want to bake a carrot cake). Instead of having to look through all the indexes you add all your cookbooks to your profile on the website.
You then search 'carrot cake' and up pop all the recipes for carrot cake hidden in your various books. Put in courgette and any recipe that has one as an ingredient is listed. Genius.