Basically when I include and use a file uploader in my form it seems to cancel out the :remote => true functionality and processes the action as HTML in place of JS. any ide
I was just faced with the same issue and found the following alternatives to make it work:
Gem remotipart => http://www.alfajango.com/blog/rails-3-ajax-file-uploads-with-remotipart/
jQuery Plugin 'jaxy' => https://github.com/adamlogic/jquery-jaxy
I think I like the first option better. But it's good to have options. =)