Lets say my optimization phrase is jumping bean bags. Now I have a page that has 15 graphics on it. If I put jumping bean bags as the alt text (attribute) for every image, can that hurt me? Can I overdo it? Do search engines really care that much about alt text?
to the best of my knowledge overstuffing alt tags is the same as keyword stuffing ... use alt text, but don't over do it.
Alt text is there to describe the graphic to those who have chosen not to view them and for those who may not be able to see the graphic at all. As long as your alt text describes the graphic and is short and to the point you should be all right. I mean not all 15 pics are of the same bean bag jumping are they. Maybe you have a blue bean bag, a bean bag juggling and a pink beanie frog or whatever. Great if they are all on a theme but not good if they are all exactly the same IMO.
I agree with toddieg. You can over do it. It is a required element for HTML4 strict and loose, though. If you are interested in fully valid HTML (WC3), you need alt tags. Either fill the alt tags in a way that is not repetitive, or use alt="" to validate.