Description:
------------
I'm not sure whenever this is intended, but is_numeric() doesn't check if a value is numeric if the value is an object and has a magic __toString() method.

I've created a patch and a test to illustrate this:
Index: type.c
===================================================================
RCS file: /repository/php-src/ext/standard/type.c,v
retrieving revision 1.30.2.2.2.3.2.9
diff -u -r1.30.2.2.2.3.2.9 type.c
--- type.c	21 Oct 2008 22:08:38 -0000	1.30.2.2.2.3.2.9
+++ type.c	8 Nov 2008 16:33:37 -0000
@@ -312,6 +312,11 @@
 			RETURN_TRUE;
 			break;
 
+		case IS_OBJECT:
+			convert_to_string_ex(arg);
+
+			/* Break intentionally missing */
+
 		case IS_STRING:
 			if (is_numeric_string(Z_STRVAL_PP(arg), Z_STRLEN_PP(arg), NULL, NULL, 0)) {
 				RETURN_TRUE;

And the test:
/ext/standard/tests/misc/is_numeric_object.phpt

--TEST--
is_numeric() should accept objects
--FILE--
<?php
class Test
{
	public function __toString()
	{
		return('1337');
	}
}

$test = new Test;
var_dump(is_numeric($test));
?>
--EXPECT--
bool(true)