This is an absolute usability must. First, your organization’s address must be on your home page, and not just in the footer like it should be on every other page. It should be big and obvious and most importantly plain old selectable text. It should never be an image which forces every user who wants to plug your address into google maps, or their address book to type it themselves instead of simply cutting and pasting.
Simple little thing, but so many people don’t do it. I’ve even violated this rule without thinking.