Playing the Online Coupon Game - and Usually Winning

I am a total sucker for discounts.  Once I've established I am buying an item, for personal or business purposes, I am getting a huge kick out of finding online coupon codes to insert at checkout.  I began to notice how many check out systems ask for a coupon or promotional code, so I opened a new window, googled the company name and "coupon" and all these sites popped up.
Just bought 25 shipping boxes.  By googling the company + coupon, a code for 5% off popped up.  In this case, that totaled 43¢, but why not?  I've scored free shipping and numerous other discounts.  All that it took was an extra minute to search coupons.  Note, though, not all codes are valid.  I just wasted about 20 minutes on a clothing site trying to insert code I found on line, none of which worked.  But more often than not, they are valid. I treat it more like a sport than a strategy.
Presumably the coupon sites get a cut if you enter the company website through their site; they often have clickthroughs.