Although [digital coupons] might look similar to the ones in Sunday newspaper circulars, many of today’s digital versions use special bar codes that are packed with information about the life of the coupon: the dates and times it was obtained, viewed and, ultimately, redeemed; the store where it was used; perhaps even the search terms typed to find it.
A growing number of retailers are marrying this data with information discovered online and off, such as guesses about your age, sex and income, your buying history, what Web sites you’ve visited, and your current location or geographic routine — creating profiles of customers that are more detailed than ever, according to marketing companies.
via washingtonpost.com (look under Business for ‘What those savings really cost you’ – the WP is not a big fan of ye olde hyperlink, apparently)
I’m never really sure what to think about this. Personally, I don’t use any reward cards or sign up for anything that collects data in exchange for offers. On the other hand, I’m not sure I see what the big problem is. So what if Amazon know what I like, how much I’ll spend and how often? They can’t force me to spend buy things. I get bombarded with ads all the time anyway, and I don’t think I can be angry because companies can target me better than ever before – it still comes down to me having self control.
halfblog.net 
The only two reward cards we have signed up for are Tesco and Iceland. Neither has resulted in any junk mail… perhaps we’re just lucky. The Tesco clubcard is of great benefit because every month or so we get a coupon for £3 – £5 which is then used to pay for my lunch for a week.
I’m a bit cagey about giving information to companies; but what I find really creepy – is when I’m simply asked for details they simply don’t need. I remember being asked my date of birth at Next. (I refused of course, bloody cheek!)On the subject of loyalty cards – I’ve heard that some of them act better as “disloyalty cards” – when the data shows that you’re drifting away they sometimes try to reel you back in with better offers designed to bring you back. Offfers you may not have had if you had stayed loyal. (I can’t testify to the truth of this; but it does sound plausible.)