It's ironic that Juliet agrees to stay and help Sawyer for two weeks, and ends up being there for at least another three years. It's a close parallel to Juliet's previous experience with the Others. Three years is long enough for Juliet to start up a relationship with Sawyer, who seems to excel at fanning the romantic flames with women who used to be close with Jack. It's this obvious rapport between Sawyer and Juliet that practically demands the return of Kate at the end.
The difficulty of women to give birth safely on the island was a major plot thread in the second and third seasons, and Juliet brings up her own failure to resolve the problems back in the future. Those issues only emerged when women both conceived and delivered on the island, so one can assume that Horace and Amy weren't somewhere off the island when the conception took place. As Juliet and Sawyer seem to agree, this implies that something changed between 1977 and 2001, when Juliet arrived on the island.
Daniel is nowhere to be found in the 1977 scenes, which could intersect with his activities in the opening sequence of "Because You Left". He could be working on the Orchid Station, given his scientific prowess, and that would position him perfectly for any upcoming attempt to turn the Frozen Donkey Wheel and return to 2008. And that does seem like something that will happen, because the Oceanic Tribe isn't supposed to be there by the time Ben arrives on the island (pretty much any day now), since he would have recognized them if they had been there!
Enough emphasis was placed on Amy and the arrival of her son to imply that her son will eventually be important to the story (or, at the very least, someone already known). There aren't a whole lot of choices at this point, but considering how connected everyone seems to be, it's unlikely to be some random child. Amy's son would be about 30-31 at the time of the Oceanic 815 crash.
Now that it's been confirmed that Jack, Kate, and Hurley have also arrived in 1977, the question is whether or not Sayid and Sun arrived in the same time period. Locke and Ben seem to have crashed with the rest on Ajira 316 in 2008, so it's not a given that both are in the same time. Sayid could be back in 1977, while Sun could have been the woman that left with Frank on one of the Ajira canoes, as mentioned in the previous episode.
Overall, this episode effectively marks the mid-point of the fifth season, and so far, the season has been hitting on all cylinders. The revelations just keep coming, one after another, and the end effect is a tightening-up of the series as a whole. It's amazing to think that all of this is still just a prelude to whatever war is coming in the sixth and final season.