Ken, as Mike mentioned, some of these issues are related to the AD and authentication environment that people are using. In my environment (full AD authentication / multiple domain, intranet), I see very little issues. Part of that is due to my modifying the code to meet my needs.
DNN has a lot going for it - in one of the recent blogs there was a CMS comparison chart. For the price and functionality, there is nothing that comes close. And yes, it is not perfect, but what software is? With it being open source, I can at least modify it where it falls short and suggest changes to help make it better. When I do modify code, I try to help others and Mike by sharing it here in the forum and/or submitting bugs with how I solved the issue. Others have also worked around these issues in a similar means. If this were not an open source application, that wouldn't be possible and at that point I would have to admit that I probably wouldn't be using AD authentication either.
I realize that your post is blowing off steam and frustration. If you are not at a level where you can step through the code and help pinpoint where the error is happening, then like any other software package, you must rely on support to have time to understand your environment, pinpoint and fix the issue. I give a lot of credit to Mike for the work he is doing. He has a lot of work with this provider in that he has to understand the different environments that this package will be used in and try to meet everyones needs.
My personnal suggestion: If your issue is such a show stopper and you are investing a lot of time in trying to work around it, then perhaps you might look into enlisting/hiring someone who has some programming experience to come in and try to solve the issue. Not only will you solve your problem, but you can help to make DNN a better application as well. You've used DNN for 5 years. For free. With free updates. Perhaps it is time to pay a little back?