Funky stuff! My only suggestion would be to let the developer set his/her own callback, in case the default output isn't what's wanted (notably tracing to something other than STDERR). update: oh duh! which is exactly what you said in the comments.. Something like:

use Carp qw/croak/;
BEGIN {
    my $logger;

    sub callback {
        my $coderef = shift;
        croak "$coderef is not a code reference, cannot use as a callb
+ack.\n"
                unless ref($coderef) eq 'CODE';
        $logger = $coderef;
    }

    callback( sub { print STDERR "Executing $_[0]!\n" } );

    sub logCall {
        &$logger( @_ );
    }
}
[download]

This gives the following output (if the example script is changed as follows):

Test::foo();
Devel::TraceMethods::callback( sub { print STDERR "called $_[0].\n" } 
+);
Test::bar();
Test::blah();
__END__
gives:
Executing foo!
called bar.
called AUTOLOAD.
Can works!
[download]

You would not believe how much I needed this code a couple of months ago....

--
g r i n d e r