Dave,

I haven't tried it out myself yet, but the last time I checked, the VB compiler for Mono was labeled as feature complete in version 1.2.3.

"Visual Basic.NET support in Mono is relatively new. The Visual Basic runtime has been available for Mono for a while, and with the release of Mono 1.2.3, the Visual Basic support will be complete, with the introduction of a self-hosting compiler and class libraries for Visual Basic development on any of the Mono supported systems."

Read about it here

Without hijacking the thread too much and in all fairness to Rainbow Portal, DNN doesn't OFFICIALLY support upgrading from 3.x to 4.x either and that's partly what the Rainbow 1.6-> 2.0 upgrade was about.  DNN is, in most instances, better than Rainbow by a good margin.  Rainbow does have workflow support built in (and has for a long time) but to me that's the only feather in the cap aside from anyones personal language preference.  The Rainbow guys will even admit DNN is well .... kicking their butts. The installed base, 3rd party modules, and active community IMHO make DNN better regardless of feature comparisons.

As for Mono, I'd like to see someone spend some time to make it happen as I think it's a bit more feasible now especially since the removal of the MemberRole dll requirements that existed in some earlier versions.

As for the whole C# topic, with the advancements in the providers and now with a better modular resource installer, I would think that it will be even easier for othersd to treat DNN as a "Black Box" and still extend it quite heavily in a language of their choice. As for reading the source I can almost promise that anyone that could read and understand the C# source code of DNN will have no problem reading and understanding the VB.Net version.  VB.Net is much more "wordy" and descriptive.