I am the biggest cheapskate going. Believe me, if I could get by with the store brands I would. Occasionally, I go back to them to see if they work and my hair is an absolute disaster.
I think it really depends on the kind of hair you have. Let's face it--there are people out there with "great" hair. No matter what they use, I don't think they will notice much of a difference.
But, I think if you are like me and have that baby fine, lightweight, layered hair, you are gonna see the difference. Right now I am using Alterna's Caviar Shampoo. I also use ISO Purifying and another ISO shampoo. They both work wonders. Any Paul Mitchell shampoo makes a disaster of my hair--so does Suave, White Rain, and Clairol Herbal Essence. I've tried the Pantene and it felt like it left a wax on my hair. I used to use Tres Semme and that was just okay. But my hair basically felt so limp.
I also agree with the other poster who said that the salon brands seem to require much less shampoo. Those bottles last me forever. I'm also lucky in that my cousin is a hairdresser and she can get all the salon brands for 50% of the retail price.