David - I looked at the other post you made and it sounds so much like multiple processors in application pooling that it's not funny.
What happens is some hosters when they set the application pools in IIS allow for multiple instances.. this happened to me last year when I setup my new server and for efficiency, my IT guy had set the application pool to allow this. I thought I was going crazy. Things would be changed, then not changed, then I'd change back thinking something was wrong, it was a simply terrible time and because I hadn't changed anything on the sites, there was no where obvious for me to look, and upon digging a bit deeper, found that this was the cause for the caching problems.
I also think there is somewhere in the web.config file you can turn off caching (I might be wrong but thought there was something - that would be a good test too if it's possible)
There was also the issue with module caching, and that generally caused problems when you were logged out, but it depends on how it's been setup.
I noticed now on DNN 4.7, the caching for text/html has been set at 3600 which is up from 1200 I think. Well that's what it was last time.
So, before you really throw it all in, why not check that your application pool settings have not been set to allow more than 1 - sometimes hosters looking at creating web farms start at this level. But for dnn users - it's just a ploy to do your head in I'm sure!
Just a suggestion but I do feel your pain and since your email is not public, no one can email you directly to ask you anything specific.
Nina Meiers
Lots of free skins... really there are