I set hotlink protection on in cpanel and put the IP of the google image servers in my list of authorised sites... crooks can't steal my bandwidth and google is able to use them... If the page ranks in the serps for a keyphrase, often the image on it will also rank for that in google image. Serounding text of the image can also help.
I've also blocked my images folder from bots in all but a few sites. It does bring traffic, but using by using tracking software I found that almost 100% of this traffic never converted (buying a product or clicking an ad) - they are only interested in taking your image and could care less about your site. There are exceptions - say if you sold something like "body jewelry" (where people are going to be interested in specific styles) the traffic can convert into sales. If you are selling "xbox" systems or IPODS (something where the appearance of the product doesn't have unique variations), I think you would find the quality of traffic to be extremely low and I personally would block the images. If people are looking to buy an "ipod", they aren't going to use image search. I don't block images because of bandwidth, but to cut down on the theft on copyrighted images and to keep my stats more accurate. If you are selling a product, froogle will bring you more traffic than image searches - and since you can submit a feed for free, image names don't matter for froogle. When possible, I would advise always making your image names relevant.
I do the same for some of my sites but others more or less open access, I just like playing games with peoples profiles.