By at least 3 companies, right here on INGO. Google Analytics, Google +1 and Quantcast (twice). And even more on other sites. I really wasn't aware of how many places were tracking me till I added the Do Not Track Plus Add-On to Firefox. It blocks them from tracking you as you browse the web, and restores a modicum of privacy to you. If you're a Firefox user, I'd suggest you download it and use it. If you don't use Firefox...well, I don't think they make a version for you, but I hope there's something similar out there for you.