Strangest thing just happend to me... I was creating an rotating banner script with php but strangely enough the banners where never showing up... no error nothing. Cleared my cache restarted my comp and it persisted then it hit me... Norton sometimes blocks images from some sites I visit... when I looked into it, it turned out that the spam and ad blocker was on... I seems that if you place an image inside a folder name ads ad or advert or anything similar or the name of the page is thus then its blocked out....
Now you may not have norton antivirus but many people do and this problem could be blocking advertisements on your sites for thousands of your visitors... Maybe we need to double check how we're organizing our advertising back end because I highly doubt that Norton is the only ad blocking program which uses similar methods to block ads...
So I guess all this means that you may have to go beyond just checking your site in 3 different browsers but also with 3 different ad blocking programs
