I remembered reading this great article on Zend on how to store data efficiently using bitwise functions, but what a mission to dig it up again.  Anyways, here it is, a method for storing multiple true/false values as a single integer. Examples of typical applications include:

• in an agenda, the ability to store various selected days in a week or month as a single int
• in a form with 30 odd checkboxes, store selected as a single int