It seems the issue has been resolved in the past couple hours (that's the last time I checked before now). I can now edit a custom screen and edit any action without any problem on the two screens I've been working on for weeks. No more viewstate messages or spinning progress indicators.
One other note...navigating the designer, saving actions and screens is significantly more speedy now. For the past week I've noticed things becoming quite slow as I tried to customize various screens. Reaction times are much faster now. In fact, Method usage in general seems more responsive just in the past hour.
Not sure if you guys were doing some app/db maintenance, making any server config changes, indexes updated or what...but everything seems to be running VERY smoothly right now.
I've been using only the stage (July) site.