Then 1.0 happens. I have now moved requests to the "thoroughly test before upgrade" pile.
In open source, it's harder because all of that is open, which means there is a conflict between x.0 means "release" and x.0 means "development is just beginning. It probably should mean the latter.
But then having a big "It's 1.0 and fabulous!" blog post is the wrong thing to do. It probably should have been "It's 1.0; be careful!" I don't see how you can have it both ways. Linus took care of that with odd/even versioning, but I think you need a huge project for people to pay enough attention to understand unless it became a de facto standard (which it hasn't in over a decade, so it's unlikely to).
(BTW, I am very grateful for the work you've put into this. Requests is truly a model API. My comments are much more meta about versioning and open source in general (using this project as an example) and should in no way be construed as saying I think you are doing something wrong.)