How often should I change shampoo?!

I usually have 2-3 different kinds of shampoo and conditioner in my bathroom. I found that if you switch once in a while, it makes your hair softer and bouncier! If I keep using the same shampoo everyday for a long time, my hair gets flat.
 
I too am a product junkie, I always have at least 2 or 3 brands of shampoos and conditioners.
I agree w/ a PP, use a clarifier once/week.
 
Listen to your hair. It can answer that question better than any of us can.

I am also a rotator. Every other shampoo, or whenever I have put more "products" than usual on my hair, I use Beyond the Zone Strip Search, a cheap clone of a Tigi product that has a lot of detergents and solvents, and is probably NOT a good choice for anyone with dry hair, or delicate color issues.
 
I usually switch when my hair doesn't like it did when I first got the product. For example, Dove shampoo/conditioner would detangle it right away when I first got it, but a couple months after it stopped. This is the signal to get a new brand!!
 
I rotate between Brilliant Brunette and Herbal Essences. I used to use just BB and my hair got dry, so I just assumed it was b/c my hair was just too damaged. One day I was at my parents house and had to use their HE and voila! silky and shiny hair. Then after a while my hair became the same way it was before ugh. So now I'm forced to rotate between BB and Vive Pro for damaged hair. I wonder what causes this need to switch shampoo & conditioner. Hair is supposed to be dead!
 
i wash my hair every 2-3 days and i switch between fekkai glossing shampoo/conditioner and fekkai luscious curls shampoo/conditioner. i have had good results and have been doing this for a few months now.
 
first off, i have straight hair

I used Fekkai Glossing shampoo but it got my hair a little oily if i didnt wash it everyday

so since then ive been using Paul Mitchell's SuperSkinny and Tea Trea. I love them both!
 
I use Herbal Essences one week and then Toni & Guy the next and it seems to be really working for me at the moment. I use the same conditioner everyday though, and once a week I use one of those great sink-in conditioners that you leave on for like 10 minutes, and I cannot recommend them enough, they make your hair soooooo silky.
 
i'm not only a label whore .. i'm a total product whore too! lol!

.. i always have 5 different shampoos/conditioners going in my shower! [ i am a hair stylist tho - so i try to keep up and try everything! ]

.. but seriously listen to your hair. nothing i say will really make a difference. some people can use the same shampoo always and there hair will always looks great .. others need change.

so, like shimma said .. just listen to your hair .. when it's time to change your hair will let ya know :]