Recently replaced lighttpd with nginx on Debian squeeze. Used spawn-fcgi to manage PHP as php-fpm is not in squeeze yet. Had a little trouble with reliability until I set a couple of environment variables before spawning the PHP processes. Since using the script below to start php all has been well.
#!/bin/bash
PHP_FCGI_CHILDREN=2 \
PHP_FCGI_MAX_REQUESTS=1000 \
/usr/bin/spawn-fcgi -s /tmp/cgi-php.socket -u www-data -g www-data \
-P /var/run/cgi-php.pid \
-- /usr/bin/php5-cgi
Next I would like to look at setting up varnish in front of nginx.