I am in the process of evaluating DNN.  A couple of fairly unique requirement that we ahve are:

• Total traffic of up to 10M hits/day. 
• One main site that recieves the bulk of the traffic and  large number (over 1000) separate "minisites" where we display content inside an IFrame on partner sites.
• The number of authors we have is quite small (less than 10) so the authoring environment is far less important than the development and production environment.

I am interested in any documents that exist on the suitability of DNN for this type of application.  The second requirement implies the ability to manage content such that it can be shared between a large number of sites and updated at a single point that would propaget to all site instances.

Any words of wisdom would be greatly appreciated.  We are currently looking at SiteCore, Ektron and Immediacy in addition to DNN. While I love the control we get from using an OpenSource solution, I am very concerned about whether DNN is really ready for the kind of load we would be asking it to shoulder.

Thanks in advance for your help!

The short answer is ... DotNetNuke is up to the task.  I think that it still is true that the website for Australian Rules Football (http://www.afl.com.au/) is the showcase for a large, heavily used DotNetNuke site.

If I remember correctly, Scott Wilhite's presentation at Open Force 2008, DSA201: AHA! -- A High Availability DotNetNuke, dealt with this issue.  I'm sure that you can get information from him, or directly from DotNetNuke Corp.