I just ordered some Wellness Core for my cat. :) I intend to make my own food for him when I can afford the start up costs, as it is cheaper in the long run, but not initially. I'd have to buy a meat grinder and supplements to mix in with the meat to start. This website has a lot of good information about cat nutrition and homemade diet and a cost analysis. http://www.catinfo.org/
I don't remember if it was on that site or another (and don't feel like re-reading now, haha), but I read a very good explanation of why dogs are somewhat of omnivores, even though in nature they are/were carnivores. Dogs have been domesticated and fed by humans for thousands of years and as such have adapted to a human diet of meat and vegetables. Cats, on the other hand, have not been fed by humans for nearly as long (when domesticated, until the recent past few hundred years, they fed themselves on mice/etc.), and as such, they're still carnivores because they haven't had that adaptation time.
I don't eat grains, so I don't intend to feed them to my animals. And I most especially won't feed them any vegetable oils. I prefer a natural approach, closer to what they'd eat in the wild. Until last week, I had no control over what my cat ate as he was in my parents' care (he's been eating Iams dry food and Friskies wet food for the past 12 years... I suppose it could be worse...) but now he's at college with me! So he's going to get Wellness. :) I still don't think Wellness is nearly as good as what I could make on my own, because it contains unnecessary vegetables/fruits that cats shouldn't ingest, but it's FAR BETTER than most, so I'm okay with it for now.
Cats have a very short digestive path, and as such, they can't digest fiber (more info on that: http://www.catinfo.org/#Cats_Need_Animal-Based_Protein_
). It's much like feeding a betta only peas...