@mslina2002 - Daniweb - interesting stuff, i'll take a look.
Re: reg pages: We only index high quality pages, at one point 4 or 5 years ago, google was trying to index around 2m pages a day - so we cut them off completely. We just index the main stuff now.
I wont stop indexing no-reply/no-answer questions, regardless of G (only a very small percent, as always with Q&A).
I think i've decided to 'just ignore it, and push on' -- in 11 years we've never benefited from analysing this kind of thing too much.
I'm clinging to what googleguy/cutts said back in the day about 'quality' winning out over everything. That strategy makes sense, regardless of these minor swings. I can't predict what G will do, or wants, or whether it will survive itself - I can only adhere to the idea that good content will eventually win out. With our without G (naive perhaps)