I just thought of something regarding the flash-forward. Walt created two batches of ricin in the course of the show - one to kill Tuco, and the other to kill Gus. Both times, the reason he wanted to use ricin was so that the murder would be undetectable. However, on his 52nd birthday, he has just got himself a .60 caliber machine gun. He is planning to do some very open and obvious murdering. Why would he need the ricin now? Who does he need to kill covertly, as opposed to the overt killings he is planning to do with the gun? Why would it matter at this point?