Well DNN performance really depends on a lot of factors. To name a few of them.
- The activity level of a site
- The use of a "Keep Alive" service (Related to #1)
- The number of modules installed
- The use of Compression and/or whitespace filters and the caching settings
- The design of the skin/modules/containers
- The hosting provider that the user is on.
To give you a bit more detail. First of all activity level has a lot to do with the load times experienced. If a site has low activity and is not using a "keep alive" service it is possible that their application will shut down and then the first request will require that the applciation be restarted and re-compiled, this can add to page load times. A way around this is to use a keep alive service such as www.host-tracker.com to monitor your site every X minutes which can prevent the app from shutting down. There are other solutions out there as well, but they involve modifications to the site and additional modules to be installed. But they do work. THis issue is actually an ASP.NET issue and not a DNN specific item.
The number of modules does also affect the load times, typically only on the main reload though as it is forced to recompile all modules.
DNN also includes functionality for Compression and White Space filters, using these items individuals are able to get better performance out of their sites. Individuals also use a module from Snapsis.com called PageBlaster which offers advanced caching/compression. Ad I just eluded to the cache settings also have a great effect on the performance of the site, if you have cache enabled you can notice better improvements.
As for module/skin/container design this one explains itself. IF you have a skin with a lot of images etc it will take longer to load period.
Now, for one of the biggest issues of all. Hosting Provider! The hosting provider can make or break a DNN site, DNN is a bit heavy on the system resources at times and if on a shared hosting provider you can sometimes see interesting performance if they do not manage their servers well. It is full possible to run a quick site via a shared host, but you have to have a good host.
For example take my site http://www.mitchelsellers.com I am running on a shared hosting provider, I just switched the first part of this week to a new host. On my old host I was getting page loads in 7+ seconds on a regular basis, now my loads are MUCH faster and I am using the same site and setup.