I have tried every single one of those fixes.
The main problem is that they actually seem to work. For instance, I put in this one a couple of days ago:
Uploads worked fine. Now today, they are no longer working. This has happened with at least half of the fixes I have tried (and all of them that have to do with .htaccess). The other half just didn't do anything.
The only one I haven't tried - and have been avoiding - is the no flash uploader plugin. It seems silly to me that I have to turn off half of a feature of 2.5 just to get the rest of it to work.
What is worse is that it appears to me that the WP folks who can fix it aren't doing anything to fix it. Any time someone complains about this problem, people point to the same post you pointed me to, but never say "its being worked on" or point to the ticket in the bug tracker.
From what I am seeing on this message board, this is a consistent, persistent problem across multiple installs on multiple architectures using multiple browsers. It is a real problem that tweaking .htaccess or turning off (or on) plugins is only putting a band aid on.