On the fly thumbnail generation

Hi & a very Happy Christmas everyone!

file_column trunk lets me do something wonderful: it can generate image
thumbnails on the fly. Need a new thumbnail size? Just pass the new
size to file_column's helper, and it'll automatically generate (and
cache) a new thumbnail.

This is wonderful, wonderful stuff, and I'm surprised that most (all?)
of the other file uploading plugins don't seem to support this, only
letting me generate thumbnails at the time the image is uploaded. When
you have a site with thousands of users and tens of thousands of
uploaded images, and you suddenly need a new thumbnail size, the last
thing you'd want to do is having to manually (through script or
monkeys) generate new thumbnails for all existing images.

So, this really is a request rather than a question. Dear file upload
plugin authors, please support this in your plugins. It's A Good Idea.

(Or tell me how blind and stupid I am, in case your plugins already do
this and I just couldn't see it.)

Thanks!

- Hendrik