I can only find one here and it doesn't work.
I really like this one: http://blog.tigion.de/2008/07/19/gimp-script-fu-photo-vignette/
and it works with Gimp 2.6 & 2.8
The first one works great, but you first need to use the selection tool to focus on the subject..
I have tried it too and it doesn't work for me. I wish this was so much easier than downloading plug ins and installing them. It should have came with the program and made it easier for some of us that aren't computer savvy. >:-[