More flexible input units (Android).
As a newcomer to cronometer, I am struck most by the little things that make the app I use now easy to get along with (although it is not without issues, or I would not be looking at alternatives!). I already posted about fraction support, which is on the web interface, so I hope it makes to the app soon.
The other "biggie" is turning out to be the limited range in input units I am offered. For example, one item I was looking at last night had a serving size of 2 tsp/10g/10kcal. I could enter an arbitrary number of "servings", or g or oz, which is great, clearly in converts between mass units. But for volumetric measures I was stuck with tsp. Since the recipe I was using wanted 125ml, I had to mentally convert. OK, not the hardest thing in the world, but surely not hard for the app to figure out for me either! Since kcal/ml can be derived from the serving size, entering an arbitrary number of ml, tbsp, cups, etc., should also be as easy as having oz alongside g.