Aqui va una configuracion funcional para WordPress 3.0 para NginX. Aunque no lo tengo activado, tambien soporta el modulo MultiSite. aunque pueda aparecer cortado por ser lineas demasiado largas, con copiar y pegar funciona bien.

server{
    server_name dominio.tld;
    listen 127.0.0.1:80;
    client_max_body_size 32M;
    #on server block
    ##necessary if using a multi-site plugin
    server_name_in_redirect off;
    ##necessary if running Nginx behind a reverse-proxy
    port_in_redirect off;
    access_log /var/log/nginx/dominio.tld-access.log;
    error_log /var/log/nginx/dominio.tld-error.log;

    location / {
        root   /ruta/al/wordpress;
        index  index.html index.htm index.php;
        rewrite ^.*/files/(.*)$ /wp-includes/ms-files.php?file=$1 last;
        if (!-e $request_filename) {
            rewrite ^.+/?(/wp-.*) $1 last;
            rewrite ^.+/?(/.*.php)$ $1 last;
            rewrite ^(.+)$ /index.php?q=$1 last;
        }
    }

    location ~* ^.+.(html|jpg|jpeg|gif|png|ico|css|zip|tgz|gz|rar|bz2|doc|xls|exe|pdf|ppt|txt|tar|mid|midi|wav|bmp|rtf|js)$
    {
        root /ruta/al/wordpress;
        rewrite ^/.*(/wp-.*/.*.(html|jpg|jpeg|gif|png|ico|css|zip|tgz|gz|rar|bz2|doc|xls|exe|pdf|ppt|txt|tar|mid|midi|wav|bmp|rtf|js))$ $1 last;
        rewrite ^.*/files/(.*(html|jpg|jpeg|gif|png|ico|css|zip|tgz|gz|rar|bz2|doc|xls|exe|pdf|ppt|txt|tar|mid|midi|wav|bmp|rtf|js))$/wp-includes/ms-files.php?file=$1 last;
        expires 30d;
        break;
    }

    location ~ wp-.*.php|wp-admin|.php$ {
        include /etc/nginx/fastcgi_params;
        fastcgi_pass  127.0.0.1:9000;
        fastcgi_index index.php;
        ###IMPORTANTE: NO PONER / antes de fastcgi_script_name
        fastcgi_param  SCRIPT_FILENAME  /ruta/al/wordpress$fastcgi_script_name;
    }
}