I can understand your frustration, but you're going to run into that with any internet software. We're using the SMF forums, which are widely regarded as some of the best around. There is a checkbox that you can check to "keep me logged in" or something along those lines -- that works just fine for me.
If you use a browser like one of the latest versions of FireFox, then even if a website does a refresh like that, you can generally just hit the back button and your text is there.
Sorry for your frustration, I've been there before, but your complaint is more to the nature of the Internet and your browser (or the lack of checking off that one tick box), rather than the forum software itself (which we didn't write). Wish I could be more help, but I try to maintain a healthy distrust of typing anything that is too long in a web browser if I can't save my progress -- browsers crash, etc, and then you're just completely out of luck regardless of any software.
I am curious what the major problem with version 3 is, though -- are you referring to the latest official version, 3.060, or the outdated 3.000? So far as I know, 3.060 is extremely clean in general, but there is always a first time for discovering a new bug.