Good because it provide images on almost every thing you search.

Not great because it doesn't provide current images present on net.

It doesn't have the options avaliable in either Yahoo or Altavista

I've used Google's image search to track down breaches in copyright. It's a godsend. I agree though that they do need to speed up times between indexing.

It's useful, but has issues. I have two primary complaints - first, the photos are often really dated. Apparently it takes Google Image Search a while to index new photos. For example, if you do an image search for LeBron James, all you get is images from him in High School. I know there are pictures out there from Cleveland, but apparently they are not indexed yet. Second problem is that broken links show up all the time. The thumbnail will be there, but if you click on the image, the link will be broken. Google Image Search should have an algo to weed those results out.