having images indexed... is it worth it?

Well I have a site where I have had image caching by search engines disabled for a long time (using robots.txt). Whenever I use a image search engine, I'm the type of person who looks at the image or saves it but doesn't really care what page it originated from. So I kinda assumed allowing search engines to index my images wouldn't help me gain more visitors. Now I'm thinking about allowing image search engines back into my site.

What has been everybody's experience with image search engines? How has it affected your bandwidth? Does traffic from these search engines turn into visitors that come back to your site again?

A site I run got over-run by google images. Increased bandwidth by 250% a month (no im not lying), increased the number of visitors into extrodinary numbers, alexa rating hit the top 10,000.

But overall, the visitors seemed to come once, then never again, so I eneded up blocking it as I was trying to create a community of repeated users, not a bunch of one off's.

Google images is okay for gaining traffic, but you have to be carefull its delivering you quality traffic and not just eating the bandwidth.