Hi Chris, welcome to the board and the Euro Forum :) It's a very interesting topic and one that has surfaced here a lot of times. Unfortunately we've never really gotten anywhere with it. This is why:
- Search engines simply wont give out that kind of information. Think about it.. it will put them on the map in terms of their size. This info is pure gold for the competitors. Look at Google - they've had 200 mio searches per day on their site for ages. It's a wee bit higher methinks :)
- If we do get some data/info - we can never be sure it's valid. If it's not directly from the horses mouth, it's not to be trusted.
HOWEVER, we do have had members posting their relative traffic data spread out on the German SE's. These findings will give you an idea of where to put your effort in terms of marketing/spend. Here's a few threads on the subject:
How to estimate a monthly worldwide search frequency for a keyword? [webmasterworld.com]
Country Distribution of Imps / clicks [webmasterworld.com]
[webhits.de...] (click Suchmaschinen to the right)
[netratings.com...] (click Top 10 Parent Companies)
Maybe not the answers you're looking for, but as mentioned, it's very unlikely we'll ever get valid data.. BUT let's wait for ThomasB to step in as he's "in the know" about Germany :)