Tomasz: One thing for you to consider is to recruit a group of "beta-beta testers", say about 10 to 20 people who you know and trust to "properly" evaluate a newly issued beta change. Send them the new beta privately and expect them to get back to you with either problems or an all clear. Then, when you issue the beta to the general population you should expect that these "experienced" folks can comment that the program is all right.
You have clearly improved the amount of documentation that you provide with the Beta's although it may be that even more is needed before most of the new user's can achieve "clear sailing". I know, you might be saying, what do you mean more documentation after all I have done?....but there could be a step by step description, augmented by small graphic screen captures, that might achieve a better "compliance" for those who do not read the current text documentation. Certainly more work on your part, but maybe this is a natural consequence of a much larger and growing user base as well as an increased amount of features and changes. I find such tutorials more effective (easier to follow) than videos of mouse movements on a screen and I prepare just such tutorials when I am trying to help some friends accomplish a specific task in AB that they are having trouble with. I usually get few to no questions back. Another thought...mayve you could recruit members of the "beta-beta testers" to write small text + graphic tutorials to be sent into to you or just published on the list. Just trying to help. Ken