As many people have pointed out here, adding a gallery to a site can stop people posting images in your main forum area. This isn't what I want as I want people to upload images and publish them within the threads etc.
What I'd love to see is a simple add on that shows all attachments in a specified area of the site. For example, the gallery page would list all uploaded images to your site, starting from the latest. The latest uploaded images could be shown on the home page or on the sidebar too.
I don't believe anything like this exists already. Would it be easy to create? I'd happily pay for an add on such as this.