With the information from other OSM members I've done a control ride on Tuesday 27th. With better position of the GPS receiver I got the same data as on 25th and therefore improved the road between bonfeld and bad wimpfen as well as the one between bad rappenau and bonfeld. Also put in some more cycleways and countryside tracks as well as a little footpath/cycleway in the village of Bonfeld.

Hey, did some nice cycling tour today and found out that my GPX data I received from the Sirf III chip was really detailed. But then I found that at some points some cycle paths beside the road would "collide" with the road.
So what am I gonna do now? I went really slow compared to a car, had two friends with me. I had the GPS right beside my head in the backpack, so connection should have been great. Didn't find anything in the wiki/FAQ section. I'll probably ride it again in a few days and test the data. If I get the same results I'll change the street (between Bad Wimpfen and Bonfeld).
I uploaded my GPX files to my account.

I love OSM! Today I've had my first mapping session and now I'll download the software to make some trails available to the general public. Thanks for this cool tool :-)