I agree with @dsitovs here that if we assign guest checkout order to email matched customer then we are blind.

Same qst: what if I type my email wrong and system associates my order with other customer?

Magneto Behaviour

When customer checkout as guest, then that means he/she want to remain anonymous with the system. However, if he/she later want to see that order associated with his/her account then it needs manual work.

There a simple extension that I have built, allows you to relate such customer with their orders. https://www.magentocommerce.com/magento-connect/relate-customer-with-order.html

I am posting this answer so that someone will get benefited.

Cheers.

I agree with @dsitovs here that if we assign guest checkout order to email matched customer then we are blind.

Same qst: what if I type my email wrong and system associates my order with other customer?

Magento Behaviour

When customer checkout as guest, then that means he/she want to remain anonymous with the system. However, if he/she later want to see that order associated with his/her account then it needs manual work.

There a simple extension that I have built, allows you to relate such customer with their orders. https://www.magentocommerce.com/magento-connect/relate-customer-with-order.html

I am posting this answer so that someone will get benefited.