In case you are dependant on advertising for making money, mainly cost per thousand impression advertisements then AJAX may not be your cup of tea as it does not require reloading of pages. In case you are dependant on page count for revenue then you certainly stand to lose as AJAX may lead to lower page count and hence low revenue.

In order to counter this structure design your site in such a manner that your ads get displayed properly and reloaded if required. Google is using AJAX confidently and making money with Gmail so why cant you. Also most of the advertisers are not concerned about the page count but the number of unique visitors flocking the site. Using AJAX would not affect your unique visitors and if you would like to improve your site visibility then definitely go for AJAX.

thnx Ades