I reviewed Zend Studio on Zend’s product page. But for weeks after, as I visited completely unrelated sites (non-PHP, non-programming), the embedded ads were often for Zend Studio. The obviousness of the tracking here brought it much more front and centre in my mind. Then Mozilla released Collusion which I installed and was quite shocked are the amount and degree of the tracking.
Watch the following short talk by Gary for more information. Then check out some plugins like AdBlock+, Collusion itself and ShareMeNot.