Audio problem: In the end of the movie when the band plays during their wedding, watch the drummer. The drummer is playing something different than what you hear.
Continuity mistake: When Walter is watching the fire go through the electrical system in the walls of the kitchen, watch the blender. One shot shows thick, chunky, white/orange stuff flowing out over the edge of the counter. The very next shot shows the blender toppled, but very clean. There is no trace of the chunky stuff in the blender or on the counter.