Robert_Charlton - 10:10 pm on Sep 23, 2010 (gmt 0)
All of the sudden we have a Y that ranks for a major traffic phrase due to social networking, viral, IBL...
Lets say X's usually shows at position 2-10 for serps.
After Y has spiked all X's get depressed to positions 8-25 for the remainder of that day to balance out the difference of what Y spiked for.
I can confirm that I have definitely seen something very similar, but I had not related it to traffic throttling. The cycling was also slower than what's reported above. Specifically, I noted this in Jan 2009, when there was a lot of concern, as I remember, that Google was "punishing" webmasters for trying to manipulate rankings, and you could never be sure whether, say, acquiring a keyword rich link would bring you up in the serps, or, paradoxically, push you down. I think the discussion was in relation to OOP penalties and to the -950.
I remember that I was seeing a site's apparently unstable reaction to a strong inbound link to home; the link had "good" anchor text, but that text was more relevant to an inner page. I compared the ranking behavior to the behavior of a balloon, where squeezing the balloon in one area would cause another spot to bulge. Here, as the phrase rankings apparently got sqeezed down for the home page, they would bulge up on the inner page.
To use another metaphor, watching the rankings on these pages over time was almost like looking at a seesaw. I didn't think of it as traffic throttling... more as a cyclic sitewide redistribution and resettling of ranking factors.
Or no traffic at all after 1 pm, day after day - even though there are 100s of visits per hour until 1 pm.
This is precisely the time-related kind of query I alluded to earlier in this thread... IMO, most definitely related to work hours, and a completely different effect from the above. I could cite other likely hours as well, but I'm under a non-disclosure not to. I assume this time-related effect does change in time zone by time zone across the country, and, I'll bet, in relevant languages around the world. I would also guess there's no change in rankings associated with this... just a change in the number of searches or bookmark clicks or whatever.