whyohwhy - 11:29 am on Aug 28, 2012 (gmt 0)
From what I have seen I have to agree with 1script.
Earlier on this year I had server problems which knocked my site out for a few days and a week after this Google demoted my site down the index causing a loss of around 70% of my traffic. I could see the huge spike in wmt when it came to page load which knocked up the average. It took 4 months to regain the traffic which suddenly came back over night, but coincided with wmt showing the page load average to what it should be with the spike having worked through the system. But it does seem to me that if you have had server issues you are put on a watch list because a recent down time of an hour caused me to lose Google traffic again for 4 days.
Maybe something else is causing this but it does seem that server down time can cause a huge problem when it comes to how much Google trust your site.