I wasted time today.
I didn't intend to - I was hopng to change an admin CRUD interface over to use AJAX scaffold - which is prettier than what I had before. But when it was all changed over suddenly all my file-uploading stopped working.
I checked to make sure all the file-saving code was still in place, the filenames were correct, everything but it kept simply not finding the StringIO that was clearly there in the form.
It took me way too long to discover that you Can't upload files with AJAX. It seems the JS doesn't accept the multi-part get/post data. :(
So I changed back...
but in the meantime (while I was checking all my code) I discovered the file_column plugin which is a neat little library that does all of your file-uploading for you. It even integrates with RMagick to let you do some speccy resizing etc. So it wasn't *totally* wasted effort... just not what I'd planned spending the morning working on :P