In the Backend Menu Orders the fields Title, user email, Date, Status, price, Paid etc are displayed.
But not the field of the person who has rented the Item (in this case the Title contains the rented item). User email is useless, if the customer has not registered in Joomla. The field date of the order is not important for rentals.
More important is to show the relation between a rented item and the renter.
Maybe it is at the moment difficult because how cck knows which fields contains the First name and the Last name of the renter if the renter doesnt register in Joomla before he makes a reservation.

We should take this in consideration of future versions of CCK. actually the whole reservation administration system in the backend and maybe also in the frontend should be reconsidered.