Disk enhanced page caching is not active. To enable it, add the following rules into the server configuration file (/nginx.conf) of the site above the WordPress directives
I'm not sure the above is quite right… what do other people see? Specifically the path to the nginx.conf file, which I don't think should be in the root.
http://wordpress.org/extend/plugins/w3-total-cache/
Looks like it's a weirdness in my $_SERVER variable:
[PHP_SELF] => /wp-admin/admin.php/wp-admin/admin.php
PHP_SELF is set twice. Freaky.
Which in turn looks like it's down to my FastCGI config in Nginx. I'm working my way through this, though no luck so far:
http://wiki.nginx.org/HttpFcgiModule#fastcgi_split_path_info