I used to work with DNN software some years ago and left it about 2 years ago.I have some experience with it. What I didn't like about DNN is that it was so unintuitive for first time non technical users. It seems even with version 6, a lot of the same issues still exist.
For one, the concept of modules and adding modules is foreign to new users unless they read the manual or someone tells them. If I create a new portal and give it to a user and tell them start adding content, they have a hard time doing it. They don't where to start.
The page should give visual clues on how to start. For example show a balloon tip and an animated arrow telling them to add a text module. Or a little video tutorial accessible right there as an overlay. These cues go away after the first time or after the app sensed the user added content.
The UI of DNN got better which is nice but it's still heavy on dropdownlists. There look bulky. A lot of the text boxes look bulky. the UI needs more drag & drop. Why not let the user drag a container from one place on the page to another instead of using a cumbersome dropdown?
The options which have actions need to be closer to where the user can see them at the location of the action. Putting lots of options inside a menu is not very useful, specially when the menu is not categorized properly and it has different contexts.
Look at squarespace.com. Instead of a boring listbox of modules, it shows a nice graphical menu. (See screen below).
Instead of action options hidden in menu, they are visible at where the user can use them (see screen below).
The DNN user interface needs to get a major facelift so it can join the Web 2.0 era of drag & drop, visual cues, inline hits and actions. I know it's getting there but the UI feels it's an inconsistent mix of old and new UI elements. I am waiting for the day when I can say it's slick.