I am arguing that a small number of things take a long time in a web server. Can you give some examples of things that potentially take a long time in a web server that are not already covered by Tornado (http client, long polling)?
Database drivers (Redis, MySQL, Tokyo Tyrant etc.) and a bad query/overheated database server can easily take over 1 sec execution, which would basically stall your servers each time such a query is run. File handling and system calls are blocking in Python. E.g. if your system call is expensive - say you are processing an image via imagemagick, very common for most web applications, then it will block your server.
