londrum - 6:40 pm on Jul 29, 2010 (gmt 0)
spreading the traffic around might be a deliberate thing. it kind of makes sense if you think about it.
imagine if someone was searching for the weather. if he's searching during the day then he probably wants today's weather. but if he's searching in the evening then he probably wants tomorrow's weather. so you'd give him two different sites depending on what time he did it.
i know that's a lousy example, but i can't think of a better one. but you can imagine that it might make sense for google to give different serps depending on the time of day.
if that's the case, then it might be impossible for our sites to stay at the top all of the time.