Though more online display ad impressions were served in November - 115.2 billion - than any other month from March to September, that was still down nearly 7.5 percent from the 124.5 billion served in October, writes MediaPost, citing new figures from Nielsen/NetRatings AdRelevance. Once again, email sites accounted for the largest share of ad impressions - 26.7 percent - up from 20.8 percent in November 2004. Portals and search engines accounted for 12.3 percent, down from 15.5 percent last year; and 11.5 percent of impressions were on general community sites, up from only 4.8 percent last year.

Yahoo Mail accounted for 16.7 percent of ad impressions in November, MySpace had 7.9 percent, and MSN Hotmail was third with 6.7 percent, whereas a year ago it was the leader with 8.8 percent.

Among advertisers, financial services were the leaders, accounting for 20 percent of online ad impressions, unchanged from November last year. Telecom accounted for 19 percent, up significantly from last year's 9 percent. Web media accounted for 16 percent, up from 15 percent.