I only take cards for stores that I frequent enough that it's worth getting their special sales flyers or personal savings because you have their card. I know it's all about tracking and advertising and selling merchandise. We're pretty much an organics household, so they can send me any type of coupons they want; 9 out 10 times, everything goes into the recycling bin because I can't/won't use it anyway. But I do use their card for the extra savings, yes.
COPPS, a grocery store by us, has a rewards program. You get so much off gas with every dollar you spend at their store. They used to use BP, but then BP started their own loyalty program and dropped COPPS promotion. So then COPPS went with Shell. So I no longer use their point system, because I don't get gas at Shell. I buy only at Mobil and BP, because that's who I have credit cards for (that get paid off every month). So depending on what/how much I'm spending (I rarely buy groceries at COPPS to begin with because they barely carry anything organic), I many times never even give them my card. I just tell them I don't do the gas savings ption.
I, too, hate when they ask for extra info at the cash register. I will answer them when they ask for zip code (it has something to do with tracking how busy the stores are), but I don't give them an e-mail or my phone number (unless it's the COPPS grocery store and I forgot my card).
And I HATE when they ask if you'd like to apply for their specific store's credit card. Um, hello? I already have a VISA card; I don't need a credit card for every store I visit. I'm trying to cut DOWN on debt, not add to it. And having all of those cards on your FICA/credit scores works against you, not for you.
Want to know the best rewards card I have? My GODIVA card! I am guaranteed one free truffle/one free peice of chocolate every month if I buy something. So my daughter and I go to the mall every month and get one free truffle and I buy one truffle. We get our treat, we've used their card, and we haven't blown our pocket book. I know they hate when we do that, but there's nothing in writing that says I can't use it that way. And we get to have a purely sinful indulgence!