Also enjoying the switch away from the case of the week. The focus switch this season means that every week what ever happens directly affects the characters as opposed to a COTW which parallels them. Excellent!
John Noble told Entertainment Weekly
(very minor spoilers):
[SPOILER=Warning: Spoiler!]“I think the fascinating thing about this season as it goes forward is that Walter has set this up by planting a series of clues. It’s like a treasure hunt in a way,” says Noble. “And the genius thing that the writers have done this year — because we didn’t want to do monsters of the week — is that we have to chase a clue [per] week. So that creates the internal story of each week because we go after these bizarre clues in really strange places. Walter being Walter, he’s hidden them in weird, weird, weird places.”
So it sounds like Walter and September prepared for the possibility that Walter's memories would be wiped, and hid the pieces elsewhere throughout New York City. I really like that because it ties in nicely with the show's theme that the past always comes back to haunt us. Only this time, it's in a good way instead of a bad way. Just as Walter in the first couple seasons was forever reassembling the pieces of his life that he'd scattered before being institutionalized, now they're reassembling the pieces of his plan to save the world, with the time in amber taking the place of the time in the mental hospital.[/SPOILER]