I found this thread to be very interesting. I especially appreciate Nina's post as it is the most objective comparison I have ever read on these 2 products. It is especially useful because it does great job of describing the issues from a non-developer perspective.
The only question I have is in regards to the comment which was raised earlier in the thread by John Mitchell. He mentioned that Joomla! is a more mature patform than DNN, even though it is newer. I have done quite a bit of research on this subject in the past and therefore I am scratching my head a bit.
Joomla! began its life as a different open source project named Mambo. It was released in 2001 under a GPL open source license. In 2005, members of the development team defected, forked the code base, and named the new project Joomla!.
DotNetNuke began its life as a product named IBuySpy Workshop. It was released Dec 24, 2002 under a BSD open source license. In 2003 it was renamed to DotNetNuke and has been evolving ever since.
So basically Joomla! is 2 years older than DotNetNuke in terms of its product life. So if maturity is measured primarily by age, then I guess I would have to agree. However, the maturity comment in the earlier post was not based on age. It actually appeared to be based on some other criteria.
If we look at download statistics, we can see the metrics for Joomla! here ( http://joomlacode.org/gf/project/joomla/frs/ ). Aside from the fact that I do not understand why there are 30+ files in the release package, if we focus on the Full Package, we can conclude that there were 186,021 downloads since Dec 23, 2006.
Coincidentally, DotNetNuke had a release on Dec 24, 2006 ( 4.4.0 ) and if we go to SourceForge, we can review our download metrics in comparison. To be fait in the comparison, lets just choose one of our 4 release package formats - the Install package. If we add up all the downloads for this package it totals ~ 140,000.
So there does seem to be a little bit more download activity on the Joomla! project. But does this indicate maturity?
If we look at marketing impact, this is where we see a substantial difference between projects. Joomla! has been extremely active in their marketing activities since the project fork was created ( fork events often create an explosion in press releases, etc... ). As a result if you look at Google Trends, Alexa, or other marketing-based systems, you will see Joomla! ranked much higher than DNN. But does marketing indicate maturity?
Lastly, there was a comment about the availability of free add-ons in Joomla!. This is an interesting comment because I think we all know that free does not always mean great value. Free add-ons typically come with no warranty or support, so although the initial price is attractive, the long term cost may be high. Compare this to the DNN ecosystem where there are a lot of high quality commercial add-ons. Because money has changed hands, there is an expectation for ongoing support which is typically a better long term business investment. So does the quantity of free add-ons indicate maturity?
I guess my point is that maturity is a subjective term which is often used without any context or criteria. And I don't think it would help much if I expressed my own opinion on whether DotNetNuke is a mature system or not, as I am more than a little biassed :).