A user gets a customer record (which has an assigned CustomerID) whenever they perform some action that requires a customer record. This includes adding an item to the cart, wishlist, or gift registry, browsing and configuring a kit item page, or creating an account. When an account is created, this becomes the permanent CustomerID for the user any time they log in. This means that you will have anonymous customer records (customer records that were created to tie a customer to some action performed on the site, but never completed the checkout process or registered) in the database that need to be regularly maintained. This can be done by running monthly maintenance from the admin section.
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