I looked around about how to send my feedback to Google about display ad targeting - as a plain searcher, not a client. I came across something called Feedback. I saw my AdWords customer support requests there only, but I used it to send my feedback anyway and asked the recipient to forward it to the appropriate people.
Of all the stuff online, I hate this (re)targeting the most. I feel sooooo underestimated and offended when I see ads about some running shoes I already bought - all over the place. Heeeey, I finished with that two weeks ago and yet you're pounding me with those ads like I'm an idiot (originally used some worse words but pulled back). I feel so retarded when I see this happening and it happens a lot.
I use (re)targeting term all the time as I wasn't sure if it's one or another AdWords feature that does it.
Well there's interest based (which Google instigates based on interests it thinks you have) and there's re-targeting, which is advertiser-instigated, and usually based on a previous visit to that advertiser's site. I (as the advertiser) set a cookie based on some defined action of yours (visiting a page or adding something to your cart) and then create a special ad to show you for X number of times after you leave my site.
If you bought the running shoes from the same site for which you are seeing the ads, it probably means the advertiser doesn't know how to retarget properly. And there's a lot of that going around.
Advertisers love retargeting because it works like crazy when done right. The operative words being "when done right".
Join the club. Last year I was in London and continued to see ads for the hotel I stayed at, for several months after my return. There was a long cryptic page I found where you can uncheck all the ad networks that you don't want tracking you. I've also read about a Firefox plugin that lets you know who is tracking you.