Originally Posted by Vick!

yes, image names are important in two ways.

1) Though they are not as important as ALT tags, but still keyword in the name counts.

2) When visitor use Google Images to search for specific image, name of the image play important role in locating.
I get approx 15-20% if my traffic from google images.

For example, search 'logo' in google images and you see a lot of logos -- Check their ALT tags, they are missing. But in file name most of the images have word 'logo'

So, its another important factor in getting traffic from google images and may be increase relevancy of page for a specific keyword a bit.