We spend a large amount of time in optimizing frontend of each site we produce. Yes, everybody knows about famous yahoo's 14 rules (plus recent 20 new rules), but how to successfully reach them is another, story.
Until today I was mislead by thought that only we have that kind of problems, but my recent try to browse www.bbc.co.uk encouraged me to write this post.
Guys at BBC use (like many other) DoubleClick for banner management. There is nothing wrong with DoubleClick, or any other banner management software. In picture below you can see what timeout did to a bbc homepage. After 60 seconds or so, page eventually loaded, but was missing banners:
On our recent project, we didn't liked the fact that ad server is slowing our page render time by 300-500%. OpenAds didn't update their banner publishing scheme for at least 5 years so we did a little trick.
There is a placeholder that holds layout and displays "loading..." msg where banner should appear. Then we load the banner at the bottom of the page and once the banner is loaded we append it to the placeholder on top of the page .
This technique works well but can't be used in every configuration. Btw, if you are using jQuery, just be sure to use v1.2 since appendTo later on contains a bug. Eventually you could patch your current with this fix.
This won't solve all of your problems, and will off course introduce new ones but will help your page render time slightly and make your visitors not so annoyed. You should reconsider how to solve bottleneck to your ad server by making a farm or something.