werty - 12:18 pm on Nov 17, 2005 (gmt 0)
mattb, the ads are there, but are only being cycled at a "1:4 ratio". That means that for every four impressions, in theory one will be an AdCenter ad and 3 will be Overture. I am not 100% sure on exactly how each one is being presented or counted, but hitting refresh 4 times in a row will not make your ad be shown. If you are getting clicks and impressions, rest assured that your ads are being shown to the users, even if you do not see the ads yourself.