The site that I am currently working on has a large number of product images. None of these had either ALT or TITLE tags. From the Google webmaster blog i found this excerpt:
“Some of you have asked about the difference between the “alt” and “title” attributes. According to the W3C recommendations, the “alt” attribute specifies an alternate text for user agents that cannot display images, forms or applets. The “title” attribute is a bit different: it “offers advisory information about the element for which it is set.” As the Googlebot does not see the images directly, we generally concentrate on the information provided in the “alt” attribute. Feel free to supplement the “alt” attribute with “title” and other attributes if they provide value to your users!”
I had not thought about about the difference between ALT & TITLE tags, but when its put like that it kind of makes sense.