Tyme - 12:00 pm on Sep 25, 2010 (gmt 0)
I can confirm that out site showed the same throttling symptoms as Drall's. Site is just over 3 years old and traffic had always been metered out until just after the mayday disaster.
It went like this.
Overall, site got x amount of traffic each and every day. For example we will say 1000 visits. The number never changed by more than 1 or 2 visitors.
The interesting part is that the home page received the bulk of the traffic. So for example home page would get 800 visitors. The remainder of our pages would receive the rest. At the end of each day we would have exactly 1000 visits. But the pages google chose to display in serps changed every day.
At the start of a new month we would almost always get a traffic bump of about 200 more visits. So each and every day we would have 1200 visits, again with the home page getting the bulk and the rest of the pages getting the rest and once agian the pages displayed in serps would change daily.
This pattern lasted for almost 3 years.
We don't know what we did, but after Mayday something changed and the traffic is now going up and down in what we perceive to be a more normal pattern. 5000 one day then 4800 the next, sometimes as much as 5800. Bottom line is that the pattern is now different.
I can say for sure that it was not link building because we haven't done any. We may have gained some natural links but nothing significant that we know about.
I tend to believe that this is some sort of a trust factor. The one thing we did frequently is change the contents and design, but not the keywords of our home page.
Hope this helps in some way.