Name Brand vs Generic

I am always looking for a way to cut costs on the things I buy without actually buying less. One way I do this is by buying generic or store brand when I can. Most of the time this works out fine.
Not today.
Generic dish soap just does not cut it. I bought Stop and Shop's new store brand from their garunteed value line. I am using at least twice as much soap every time I wash dishes. So yeah, I got the same amount for a much lower price but I am using so much the cost difference is almost unnoticeable.
This has inspired me to compare other generics and name brands. I am interested to see when the only difference is the price cut and when there is a difference in how well it works. With milk I notice no difference in taste. In ice cream there is a large difference between the brands. With diapers, it depends on what store or generic brand you are using. I have found that Target diapers do not work well, but WalMart diapers are fine. However I usually stick to Luvs becuase they work perfect for us.
I am looking for suggestions on things to compare. Where is it worthwhile to buy name brrand versus generic and when is the only difference in the price?
Suggestions?