Toiletries - What Say You?

So, one of the perks of going crazy with coupons and entering just about every giveaway/sample offer I can find is getting lots of stuff.  Especially toiletries, because so many of them are offered as prizes from magazines and online giveaways.

Now, don't get me wrong, I love having all this stuff for cheap/free.  But the problem I'm having is that when I get something new, I want to try it right away.   Therefore, I wind up opening and using multiple products at the same time, haha.  Seriously, I currently have four toothpastes, three leave-in hair conditioners, a million shampoos and conditioners, and a handful of face lotions in circulation as I write this.

But when it comes time for me to figure out if a certain product is working (say, if I want to buy another one of a product), it's difficult for me to know which product is actually working.  This might not be an issue for say, toothpaste, but for specialty brand face products that normally cost $40+, it can be an issue.  What I'd like to do is to stick to one product at a time (instead of using something different every day) for a little while to check how things go.

So here is my question to you folks is:  How long do you try out a new product to decide if it's right for you?  One week? One month?  Or do you just hope for no bad reactions and don't care if it's be best product for you?  Please let me know in the comments!