Some browsers won't send the application/json mime-type to HTTP_ACCEPT header when dealing with some tricks to enable Ajax file uploads:
https://github.com/blueimp/jQuery-File-Upload/wiki/Setup#content-type-negotiation
It would be interesting if Rails could take care of it transparently by checking for the HTTP_ACCEPT header before rendering a JSON response with the 'application/json' content-type.
When 'application/json' is missing in the header the json content would be rendered as 'text/html' for better compatibility.
How does that sound like?
