Thanks, works great!

As far as I remember I didn't erase the memory when changing the log format, maybe this was a problem for mtkbabel and Datalog (but on the other hand I changed the log format with Datalog which seems to erase the memory after changing the options).

Anyways, I'm using BT747 now which seems to work more or less. Thanks for the advice.

Mtkbabel uses the specification which was created by the bt747 project, so theoretically there should be no difference. But I think that it wasn't a software issue, because it seemed the device didn't record any data, maybe because I changed the logging format(?).

But Datalog seems to be a very poorly engineered, this suggest, that this is true for the device too. After several attempts I succeeded in erasing the device and restoring the default configuration.
I did a small test run and everything worked, so I think a can use the device now, even if the reason for this issue remains unknown.

What really annoys me is that the device doesn't have a display that displays status information, time and location. When I bought it, that didn't seem to be a problem for me, but now I think it would be nice to have one (especially because the LEDs indicated that is was recording).

Well, now I have to take like it is and currently it seems to be working ;) and I hope I won't have any problems with it in the future.

Meant notes in a broader sense (audio recordings, pictures, etc) ;)

I wasn't concerned about the quality, because most of the data matched with the already existing roads. I just drove on mainly traced roads with a long logging interval (5 seconds) and didn't take any kind of notes, this is why I thought it was a bit useless. Anyhow I think I could complete some roads, even if it maybe needs later refinement.

Well, at least the proprietary version doesn't ;).

It turned out to be a Java bug:

$ java -version
java version "1.6.0_06"
Java(TM) SE Runtime Environment (build 1.6.0_06-b02)
Java HotSpot(TM) Client VM (build 10.0-b22, mixed mode, sharing)

This fixed it (as proposed by http://www.suckless.org/dwm/manpage.html):

$ export AWT_TOOLKIT=MToolkit