Here's my little updated contribution - it prints colorful output in the way I prefer. Define a helper function isRootIp() that contains an array including your IP; then calls to bt() simply return, so you can sprinkle backtraces in live sites w/o anyone knowing.
<?php
function bt()
{
if( ! isRootIp() )
{
return false;
}
array_walk( debug_backtrace(), create_function( '$a,$b', 'print "<br /><b>". basename( $a[\'file\'] ). "</b> <font color=\"red\">{$a[\'line\']}</font> <font color=\"green\">{$a[\'function\']} ()</font> -- ". dirname( $a[\'file\'] ). "/";' ) );
}
?>
