Back on page 1 wolfpaulus said
The last thing that needs to be done is adjusting the Arduino IDE preferences file: ~/Library/Arduino/preferences.txt on the Mac and C:\Documents and Settings<USERNAME>\Application Data\Arduino\preferences.txt on Windows:
The build.f_cpu preference needs to be set to 1000000L
I see that on Linux "preferences.txt " is in the library directory and I could find no mention of "build.f_cpu".
Is this now obsolete ?