I've not experienced anything like that. I don't think they have any type of pop ads on this site. Have you scanned your system for adware lately? What you are describing could be caused by adware, which is triggered by the keywords on our site.
Can you tell me what page you were on when it happened?
Was it on the main site or the forum?
Do you know what the product was that was in the ad?
What browser do you use - IE, Firefox, or something else?
I'll pass the info along, and this will help track it down if it came from here.