Companies like zdnet which depend on advertising for their revenues often embed links to either, or both, ads and counters, on internally hosted or third party sites.
One immediate consequence of this is that when ads.doubleclick.com, cache.blogads.com, ads.adbrite.com, i2.ytmg.com, or i.i.com.com have a problem, so do readers waiting for page loads.
There are two main things going on there. On the internal side companies which run many different web "properties" usually prefer to host ads and images intended for multiple channels in one place. This reduces complexity, and thus both work and risk. On the external side some advertisers demand third party page read information.
In my own case, for example, I sometimes embed images hosted on my own site in these blogs just so I can track readership independently. Over the last eleven months, for example, I've accumulated 110,683 records like this one showing someone reading my blog for April 7, 2006:
XXX.XX.219.27 - - [26/Sep/2008:09:19:15 -0600] "GET /images/apl.gcd.jpg HTTP/1.0" 200 10740 "http://blogs.zdnet.com/Murphy/?p=568" "Mozilla/5.0 (Windows; U; Windows NT 5.1; fr; rv:1.9) Gecko/2008052906 Firefox/3.0"
Some of the security directions, specifically those with respect to cross site scripting limitations, anti-phishing filters, and non recording modes, being taken in the IE8 betas suggest to me that this kind of thing has a limited future - because we're clearly headed toward a future in which any page not wholly loaded from the same server at the same time isn't trusted.
If so, there's an obvious big system solution for publishers and advertisers: split the properties as Apache virtual servers but actually use one big machine for everything - and meet advertiser needs by having it write the appropriate log records directly to third party remote hosts.
Right now, however, I don't know of a small system solution that would actually work well - and that, I think, suggests a hot little niche for someone willing to take it on.