Have you looked at AxCMS? (http://www.axcms.net).

While I am not a DNN expert as yet I am very familiar with Joomla/Mambo and Drupal as well as several commercial CMS systems such as Ektron CMS.

DNN does have a commercial CMS module available though the developer escapes me.

From my experience thus far with DNN it really does not lend itself to what at least I am used to in CMS systems. That is to say Workflow as well as filtering etc. It is not as efficient either if your looking at a high traffic environment as the various others I have noted.

DNN indeed has many many strengths as you noted and it also suffers some weakness in that you never know if say the CMS module you purchase will function with a new release of the core framework or even whether updating to a new release will result in problems such as loss of data due to the CMS etc. We too have a few projects we'd love to use DNN on that are candidates for CMS but we decided to go with Joomla on them because we know it's capable of handling the projects as well as future expansions if need be.

The thing that sux about Joomla/Mambo is the learning curve for NoOb's. Trying to teach someone to effectively administrate a Joomla site can be very painful. If however we administrate it and all the client need concern themselves with is content creation, workflow to live publishing that part is not horrendous.

DNN can be "skinned" (like any CMS and most portals) to give you the look you desire.

As to the C# end of things... If Umbraco is .Net 2.0 compliant then you could in theory develop in VB, C# or any other 2.0 compliant language as .NET uses the CLR (Common Language Runtime). VB 2005 is in fact basically a butchered C#. Many (many many) VB developers have hopped shipped to C# as C# is more versatile allowing for multiple inheritance etc. (be MH a good thing or bad :) ).

You'll find on the Internet alot more development support now for C# than VB, just a fact of life. Still, either way as long as the compiler outputs MSIL code .NET can cope with it be it VB or Cobol.

Standards and code validation is another matter. First off this stuff always seems to have a level in flux of whats really important compliance and not. Standards are often in a state of flux and browser standards compliance is usually in worse shape than that of the expectant standards. For example, with DNN we have witnessed Firefox drop menus under content making the menu unavailable. Opera doesnt like the built in editor. AOL had contortions with a few modules we purchased (and then gave up on using PHP scripts hosted in DNN iFrames instead), MSIE we've yet to see any issues with that I am at least aware of.

You need to ask "WHY" do we want to be standards compliant beyond the obvious of, "Should'nt everything be standards compliant?" LOL. Standards move and standards are often not met.... so.

I too prefer ASP to say PHP which Joomla/Mambo use. Generally speaking we go with whatever will do the job effective like and provide the extensibility necessary for the future preferably without us having to write custom code to do so.

If you really want have some fun... while I have not used it now for several years Ektron CMS used to be available for a 30 day trial. We did some work with it for a few financial entities and Citizen utilities. This is the closest thing to CMS done right I personally have ever toyed with. It isn't cheap. You will see a list of pretty impressive clients/installs at the site.

"COMMERCIAL" software for serious things that deal with the net tend to be full client/server apps which is how it really should be. A author should never have more than a client piece of software on their PC. They write, they submit. It comes back for edit if need be etc. From point of submission be that to a editor, proof reader, publisher on and on they should have absolutely no concerns of beyond the content. They need not know how any other process works.

With that said, DNN would be DYNAMITE as a true C/S app.

"create, edit, approve, and publish"
There are many great developers out there with affodable solutions.  Those that offer subscription services are the best value IMHO.   Take a gander at Snowcovered.com, and the DNN reviewed modules at the DNN home site  to get an idea of what is possible and available for DNN.

I started with 1 demo intranet and now have 5 intranet sites ranging from CMS to project management and reporting all running DNN with AD authentication.  This was a minimal investment compared to purchasing several commercial solutions and they all work together very well.