Hi,

I believe there's a mistake in the Rack:Sendfile documentation @ 
http://rack.rubyforge.org/doc/Rack/Sendfile.html

proxy_set_header   X-Accel-Mapping     /files/=/var/www/;
should be
proxy_set_header   X-Accel-Mapping     */var/www/=/files/*;

Thanks,
Carlos