I got the downloadable New Fitday, so I thought I'd post a review of it, in case anyone else was curious.
Pros: You can track a lot more stuff. There's even a graph that displays "mood vs calories consumed." The weight goals and tracking is much more advanced than the online version. They have a section where you can customize ratios of fat-carbs-protein% and set goals based on that and display how closely you have stuck with it (which is cool, because it's doesn't have the low fat diet concept and limit how much fat you can put). The format is slightly different, but not so much that someone already using fitday online couldn't learn it. Oh and my favorite: you can make custom foods based on other foods--like drag and click ingredients from a recipe, etc. There is a specific field for measurements with guidelines on how to take them.
Cons: if you already do fitday, there's no way to download it into the PC version, so you'll be starting all over again. It also freaks out if you want to just type in something and put 1 carb...it wants to know what it is and wants you to set it up as a food...so no random carb additions. Oh and other people can't look at your fitday offline.
Overall, I thought it was worth the $20 to download, considering I've used it free online for so long.