Checks if the current post is a custom post type, returns boolean

is_custom_post_type.php

<?php
/**
 * Checks if current post is a custom post type, returns boolean
 * 
 * @author Joshua David Nelson
 * @link http://joshuadnelson.com/code/is_custom_post_type/
 */

if ( !function_exists( 'is_custom_post_type' ) ) {
	function is_custom_post_type() {
		
		// find custom post types
		$args = array(
			//'public'	=> true, // -- uncomment if you only want "public" cpts
			'_builtin'	=> false,
		);
		$output = 'names';
		$public_custom_post_types = get_post_types( $args, $output );
		
		// if there are no custom post types, then the current post can't be one
		if( empty( $public_custom_post_types ) )
			return false;
		
		// access global variable
		global $post;
		
		// get the current post type, returns a string or false on failure
		$post_type = get_post_type( $post );
		
		// check if current post type is a custom post type
		if ( $post_type && in_array( $post_type, $public_custom_post_types ) ) {
		        return true;
		} else {
		        return false;
		}
		
		// if all else fails, return false
		return false;	
		
	}
}