Well I only have about 30 or so sites and the effects for me have been quite random as well!
Some of my new EMD's are ranking nicely, while older ones are being pushed down to below 100. Other new EMD's that were nicely ranking before have been pushed down as well. Some older EMD's that are ranking in 1-3 spot have not changed at all.
All of these sites have been built with pretty much the same exact structure, and promoted using the same link building techniques.
I, also, am unable to find any method in this madness.