This isn't really about Adsense, but the logic should be the same. I'm using an ad network that sends ads out to multiple providers (including Adsense), and returns the highest bid.
Occasionally, though, I've noticed that ads can take up to 30 seconds to load. In the meanwhile, all I see is a blank box. Site visitors have mentioned this, too, so I know it's not just me.
I ran a scan with an online tester (not sure if I'm allowed to link it here), and it showed my page load time was 2 seconds, but the "document complete" time was 24 seconds! The big delay (22s worth) came from Fastclick, which I assume is one of the networks.
The difference between what Analytics says and what the ad network says is about 30,000 pageviews a day, so I think that this is really adding up to cost me money.
Can you guys suggest any methods I can use to make the ads start loading sooner and/or faster? Pre-loading, caching, or something server-side to catch a delay of more than a few seconds (to kill it and refresh, or at least kill it and show something else)?
I guess that I could just disable Fastclick in the list of networks, but I hate to do this because that might have a significant impact on my RPM.
I'm also worried that as soon as I disable Fastclick, another network will be a problem, so I'm hoping for a better solution that I can do on my end than just disabling slow responders as they're found.