Recently we got project about magento what require to lock all of guest access. The site only accept user logged and all of pages in magento is private for users only. That mean we have to the member only magento site.
In addition, we can build a welcome page or any page base on logged user from this article. Now will show you how to check and get user information.
From everywhere in magento code you can check login by this code line
You may want to know full information about the current customer/user. You may check this debug code
$customer_data=Mage::getSingleton('customer/session')->getCustomer(); echo "<pre>" print_r($customer_data);
Or you can get customer information via help instead of Singleton object
It should return the same result data. Good luck for your coding