At last, a good samaritan (fadden, whoever you are, big thanks !! ) helps me find the solution for my traceview problem.
And actually, I can't imagine how he find it !
The data created by the Debug.startMethodTracing / Debug.stopMethodTracing pair only works when the debugger is NOT attached !
You can still launch it from Eclipse, but when the data file is created eclipse can't be used as a debugger ( though it still can be used as a way to get the log !).
I launched Eclipse, then my application ( so it started the emulator - with a -sdcard optional parameter ).
Then terminate my application with Eclipse.
At this point, I could use the android interface to launch my application, go to the part I wanted to profile, and generate a valid .trace file !!
I could get it from my emulated SD Card with the Eclipse DDMS perspective, and launch traceview with this file, and at last have a correct result (and quite interesting... More on that latter )
Thanks again fadden !
On a side note, one could be a little worried by a debugger that produce a different behaviour - in this case a different file - than the without debugger case.
For now, I will just close my eyes, and hope it is just in this case ( famous last words again ? )