I've used it a couple times. I've changed a couple things:
1) Made it only add the extensions held in $this->image_extensions and $this->swf_extensions. I thought about making a new array of bad extensions but that list could get big so I am just specifying which ones I want to be added.
2) When I click on the image, I want it to display the image in real size. Quickly, I modified it so that it just opens a new window. I suggest maybe adding a link that executes file_browser_show_img_dlg_<?php echo $this->disp_browser_id; ?>() and is configurable if you want that feature and when you click on the image it pops up in a <div>. This would keep the GUI simple to use as not everyone (such as visitors) don't want the forms to edit it.
Just a couple suggestions otherwise I love the idea of this!