I am interested in knowing the limitations people have experienced with using DNN for the implementation of complex web applications.

I am being told by some software vendors I want to hire that DNN isn't as useful as asp.net mvc when it comes to implementing web applications. I press them for details on what type of functionality is either not possible or not effective in DNN, but they can't explain it other than to say "our developer's prefer MVC" or "DNN is fine for portals, but not for applications".

I have done several DNN implementations in the last year, ranging from simple CMSes to adding interactions with remote databases. I have found, once the learning curve was overcome, that I am able to produce straightforward websites with specialist database interaction through custom modules fairly quickly and easily. The rich infrastructure and component-based approach is why I have gone with DNN rather than the "build it all yourself" status of the current ASP.NET MVC offering.

I have no doubt that programmers love MVC because they have to lots of fun coding to do to achieve things, but this isn't the sort of decision criteria that makes a board of directors feel good about a long term spending strategy.

The ASP.NET MVC approach is clearly popular amongst developers who would have been writing ASP.NET web applications without a framework like DNN or SharePoint, so I am not trying to compare it technically with ASP.NET webforms. I know all the arguments of ASP.NET vs ASP.NET MVC very well and can see both sides. I am just trying to work out where I will meet limitations when using DNN as my application framework.

I don't want to make strategic business decisions based on what developer's do and don't want to do, so I am really interested to hear about people's views (from experience would be good )  on what type of applications are suitable and more importantly, what are not suitable for implementation in DNN.

I would use DNN (or Sharepoint) as a CMS system. Not for creating web apps from scratch. You will have to learn DNN inner workings and you will most probably hit a wall where you will fight DNN because you're bound to its framework.

Create web apps from scratch and borrow code from other projects. For example, if you want to implement a membership system, use microsoft's asp.net membership framework. Without DNN, the whole world is open and you can use whatever you want. DNN is based on Webforms. I don't know how it can mix MVC but I am sure it's not a good idea. If you want to use newer technologies like LINQ to SQL or LINQ to Entities, MVC, different models, you will end up with a hybrid system with different types of data layers and business laysers which will be hard to maintain. What if you have other developers who come after you to maintain your system and who don't know DNN? It becomes hard.

You didn't explain your advantages from using DNN. Your decision will depend on your requirements. If your app needs to have a lot of CMS functionality, DNN could be a good choice. Otherwise develop it yourself.

AFAIK it should read "Webform" instead of "webfarm".