There is another cool hack for savings $$$ on international flights: use your favorite meta-search or site like CheapAir first, then submit your finding as BeatMyPrice to http://flystein.com - expert flight hackers will try to beat your price and in most cases they do beat it by a lot!

Its almost impossible to get good quality results all the time in automated way. Professional travel hackers use many tools plus human brain to save on flights, one simple site could not magically save you all the time - if it would be so easy sites like kayak would do it too :)