I'm using it for our company's intranet Portals... it is, hands down, the worst experience in my 10+ years of web design.

Almost anything you want to do seems to require an enormously annoying work around...

It's trying to be everything to everyone, and instead it just makes everything way overly complicated.

If you still have the choice of not using dnn, choose that.

I used to love web programming, but over the past year, I've grown to hate it.  I may very well change jobs once I finish this project if I have to continue writing for / managing dnn sites.

Horrible.

 I use DNN to provide web applications to clients. All of them have loved what I've been able to deliver to them.

DNN is excellent in these ways (for me);

It's pretty. I SUCK at graphics, so any fully custom site was all straight lines and looked, honestly, terrible. DNN makes it quick and easy to get it looking pretty with the purchase of a skin package.

It takes away any hassle of dealing with anything except creating the content for the site. I don't have to make the menu system, or update other pages to include new pages. Or deal with programming a menu system for my site, ect.
The same goes for security roles, security, logging in, user creation, ect. DNN takes care of all the 'website' maintaince issues so I can focus on producing the content my clients require.

DNN makes it so I can spend more time producing what my client wants and less time fixing pages/menus/users/security issues.