This is the build I use just about every game, and it doesn't lead me wrong. That said, I have not tested in in ranked (as I just leveled up to 30). The idea of the runes and infinity edge is to max out your damage capabilities and then youmuu's ghostblade to penetrate their armor. Phantom dancers can be substituted for boots and add to your attack speed, and indirectly your damage. The 50% lifesteal you get from full stacks on the bloodthirsters allows you to heal pretty quickly (a quick trip into the jungle is a full heal late game) and add greatly to your sustain during a fight.

Sorry it is so short, I may come in and add more if I remember, but no promises.