Christian you cannot just do this everywhere. The single line is only possible if the parameters is not to be computed or creating new objects.
So the ones who creates a new Object for the parameters etc, should still be guarded with the isDebugEnabled etc.
Also some of the operations on the parameters may take time to compute, so its really not always a good idea.
IMHO the isXXX should be used when the parameters are not simple and if they invoke operations to get data (and the operation is not a simple getter, the compiler can inline).