Hi purplebox,
I've noticed that this site is running on DNN 3.2.2 as well. I have been using DNN 4.x and have had great success with it. I've put together the steps I used to update to DNN 4 from a multi-portal DNN 3 and can post it if there is an interest.
I see that there are more and more DNN 4 sites up and running, and would imagine that the Core Team members probably have their own upgraded, simply because you get to use the new features of ASP.NET 2. If I had to guess, and this is soley a guess, one reason this site has not been upgraded yet is simply because of priority. Another reason might be to keep this site in DNN 3 because there are still DNN 3 enhancements being made and this site would serve a useful purpose for testing backward compatability as new modules are being developed.
DNN 4 seems to be very solid but if you are thinking about updating to DNN 4 which uses ASP.NET 2 (optionally SQL Server 2005), and you have many 3rd party modules, you may want to look into the possible pitfalls that may affect your site. I ran into two:
1) Hosting providers supporting ASP.NET 2 will normally use Medium Trust in shared environments. For the most part everyone benefits here, but if you have modules that need higher trust levels, your module will thow a security/permissions error. You can easily change your local environment's trust level via Start > Administrative Tools > Microsoft .NET Framework 2.0 Configuration. By default your local machine is setup with Full.
2) You may require your hosting provider to make full database backups for you. The import/export utility in SQL Servers Integration Services allows you to backup the tables and data within, but not the relationships, stored procedures, etc. Red Gate's SQL Packager provides a solution for this but it costs, http://www.red-gate.com/products/sql_packager/index.htm