On an unrelated note I've turned back to cash only for my day to day transactions. Looking at my bank statement it details where I'm going and what I'm doing. The restaurants I visit, which days I go to the movies, which supermarkets i go to, how frequently i go to each and how much i spend, petrol stations, toll gates... Lots and lots of behavioural data. Makes me uncomfortable...
I find that advantageous, personally, and try use my card rather than cash, because I then have a record of my spending which I can analyse, import into my budgeting/financial software etc. It's easier for me to manage my finances and budget if I can clearly see a bigger picture of where my money is being spent. It's easier to just download a bank statement that to record each and every purchase manually. If I thought anyone else was interested in this stuff and could easily access it, it would make me uncomfortable too, but I don't think anyone is!