Question

How to find checkout method is whether “guest” or “register”.

getCheckoutMethod is deprecated.So is it advisable to use it.

Answer 1

and where it is deprecated? latest magento 1.7.0.2 seems to use it and define it and not mention anything about deprecation of this method

Mage::getSingleton('checkout/type_onepage')->getCheckoutMethod();

this method is defined in multiple places

grep ' getCheckoutMethod' app/code -rsn
app/code/core/Mage/Checkout/Model/Type/Onepage.php:165:    public function getCheckoutMethod()
app/code/core/Mage/Paypal/Model/Express/Checkout.php:661:    public function getCheckoutMethod()