I have Piwik 2.4.0 installed on a Debian 7 server with Nginx and MySQL.
I am certain I have the correct tracking code; I verified by re-copying from the settings in the web console.
I am looking for any reports from “Today” or otherwise, and none display. The table piwik_log_visit remains empty, but other tables for Piwik configuration, etc. are appropriately populated.
I have no bootstrap.php and no particularly strange settings that I can think of.
Nginx logs do not reveal anything anomalous that I can determine.
My Nginx configuration: http://paste2.org/PNyOUjHs