While I agree that 2.1.2 was a fast build, the reason I was keen to move away from it was because of the XML file created in the logs and sometimes the xml log file got so big due to whatever problems it caused hell on my server. However, I'm running quite a few 3.1.1 builds and have found that it's also a very good build.
3.1.1 was the build that I felt had the most time spent on fixes before releases, wasn't in preparation for running on aspnet2, had the longest time between builds I think - between 3.2.2 for example (just going on memory) and gave developers a longer time to polish and refine their own modules I believe.
I tried to upgrade my site from 2.1.2 to 3.2.2 and it was the demise of 3 weeks of my life, if not more. It's still got ongoing problems, due to a bad start with a module supposedly designed to import members, but I will live with that for now.
However, I'm torn between having such a nice Catalook build and 3.2.2 on one site that really performs well.
Overall, 2.1.2 was built for speed, with xml the downfall when the logs got too big, if they weren't deteled on a regular basis or set to delete in the scheduler and 3.1.1 has been the best build for me in regards to installation and modules available, since it did start with a newer interface, more functionality with the modules and such.
I don't upgrade my portals, I've never found it goes smoothly and often hear of developers with ongoing small issues they end up living with. And I don't think it's a reflection on DNN, if you have a stock standard installation, I think upgrading will go pretty smoothly, but most portals do have an element of customisation in them.
And as much as I hate upgrading, I can't wait to get some of my key sites on 3.3+ / 4.3+ when it's stable, and found that I do like the features of the new custom provider - I think that alone in itself is such a huge step forward in making DNN a first class product. I really hope as much time is spent in stabilising this build as was spent with 3.1.1 and while it's difficult times now (yes dnn has been, for me, in the last month - really very frustrating) I genuinely believe that this is going to bring more developers in to using DNN as their choice of development environment, and that in turn, makes DNN mature further.
It's hard living on the edge, but I'm finding more developers with some amazing talent who have only worked in DNN3, they've never installed DNN2.
Just my thoughts on the matter, since I've been running with DNN since 1.09 days and providing solutions, based only on DNN since late 2002, ran and managed servers, worn and still wearing the pain of every problem build and still moving ahead. I recently purchased dnnskins.com and it's dnn 1.10 and amazed and how sophisticated it was at the time. Even modules and reports we don't see in later builds, for various reasons, and all in all, it's a little rocket considering what it's got to do.
Nina Meiers