Reusable items do not have charges, and generally an item that has a Use: description in the tooltip but has no charges listed in the tooltip is reusable. There are probably exceptions; one that comes to mind is an item that completes a quest is essentially not reusable no matter how it is described. If they do have charges, they are not necessarily destroyed at 0 charges and can be refilled/recharged in some manner, much like several pre-BC goblin engineering items.
To mitigate the power of such an item, reusable items generally have a cooldown during which they cannot be used. Items with insignificant affect on gameplay may not have a cooldown.