Interesting. My PhD research is on precisely this topic-- nutrition diaries + machine learning for identifying the effect of foods on people with chronic illnesses, such as Crohn's or MS.

I think this site is a good idea. It'd be even better if you could add in amounts and somehow standardize the entries. Even better still if you could break foods down by ingredients.

Also, if you get a few users and want to have someone analyze your data in super cool Bayesian ways, email me!