Was just wondering.. because in the last few weeks or so, I've bought several new hair products, mostly shampoo/conditioners. But I rotate what I have, and I don't shampoo every day....... so it's all probably going to last for quite a while. Anyone know if there's a "rule" of how long you should keep a shampoo before tossing it? I mean, does it "go bad" after a certain period of time? When I say "go bad," I mean does it lose effectiveness or whatever?