@maximus - from your valued input and that of other experiencing the EXACT same symptoms, I guess we can pretty reliably say that our reliance on Google traffic is our downfall. The trick now woul dbe to fid out the "why". As far as I can tell, these yo-yo periods occur around announced major algo changes. If Google was doing minor changes in early to late January (they say the do them nearly every day) then those had no effect on us.
One other question for you max: When the light is RED, do you notice any significant position changes in your B & C sites? I don't. This is were the is a complex paradox. SERP's "normal", traffic junk.
BTW tedster, the vast majority of my site traffic in the past few days is coming from the US, which is normal. I do see a pretty dramatic dip in visitors in GA.