Shaddows - 4:07 pm on Apr 2, 2012 (gmt 0)
Sure there are macroeconomic factors, but in addition, we have different refferal profiles. Whenever there is an ecom shakeup (@ohno and @backdraft are the perfect markers for this happening), we get 3 different referral profiles cycling. One is "normal", one is zombie-ish, and one is counterintuitive ("Let's see if people like THESE pages- even though there's little traffic and precious few IBLs").
They used to take 2 weeks to cycle in and out in phase-shifted wave patterns, now they are on different and much shorter periods, causing fairly chaotic traffic stats.