Last week I bought a top from M and S. (In-store, not online)
Tonight I was surfing a favourite website (TV Tropes) and there was an advert for the EXACT same top.
DH pointed out that I had looked on the M and S website - probably looked at about 40-50 tops on there - and the search engines know what you click on. He said "coincidence".
Then I came on Mumsnet and there was an advert for M and S - with the same top. I know the Google sees what you surf, but I didn't buy the top online - I bought it at the shop!
So - why - how do they know? Has Marks and Spencer sold my info? But no, my debit card isn't linked to my online activity.... ??