That is a great question, and I would love to hear the "official" DNN response because I see some very large DLLs in the file system that could certainly be contributing to slower-than-should-be page loads.
I have noticed that our sites are initally very fast, but as more and more modules are added, they tend to slow down regardless of the website size or traffic. It just seems that more modules=slower sites.
I have tried things like PageBlaster and other products that are "Guaranteed" to improve site performance with absolutely NO noticable performance increase.
The guys at PowerDNN (where we host our sites...here's a free plug for you Tony!) have a control suite that seems to clear out the site memory or caching or something (not sure what it does exactly), but REALLY makes a difference in the way the sites perform when they start running slowly. I have seen some of our sites, like http://demo.schooldesk.net, which is a demo site of ours that has over 50 modules in it, just come to a complete crawl (I assume because of all the huge DLLs in it), but when I use their SIte Optimizer in the PowerDNN Control Suite, it just works! Everything goes faster and STAYS faster for months. BUt eventually, I see things starting to slow down again, so I have to run the Optimizer again.
If this Site Optimizer really works as well as I have seen it work, can anyone tell us what it does, how it does it, and why an equivilent of it can be built into DNN to automatically Optimize sites all the time?
May as well get a shameless plug for our new site here too: www.servesouth.com