Ambivalence on the right could also explain some of it -- was turnout low in right-wing strongholds? Are there time-frame issues, too (i.e., when were the polls taken)?
National Public Radio in the US the other day claimed there had been a big swing away from the CDU in the last few weeks due to Hurricane Katrina -- it supposedly enabled the left to portray Merkel as a know-nothing, antigovernment Bushite who would leave Germany similarly vulnerable to disaster...
But you mention turnout - a very good idea, come to think of it. I looked up, and indeed you are right: in the (left-voting) East, participation generally increased, in the (conservative-voting) South, it fell. Tough, all of these changes are of a few percents, I'm not sure that explains it all. (As for timezones, Europe is small :-) from the English Channel to the borders of Romania and Ukraine, it is all one timezone: CET, which is GMT+1, or ET+6.)
As for a Katrina effect and campaign in Germany, the first time I hear it - but someone closer to the pulse should decide on that. *Lunatic*, n. One whose delusions are out of fashion.
