1. Jack and his crew of strandees are armed to the teeth now. There was a whole cache of guns down there with Desmond, everything from pistols to rifles to shotguns, Kate has already grabbed a shotgun, and I think just about everyone is going to be armed now.
2. Food will not be a problem for a long time. That was quite a bit down there, and as long as they still hunt to supplement it, it shouldn't be a problem. But we all know there is going to be a huge fight over it anyway, I'm sure.
3. That crew that came up on Jin, Michael, and Sawyer and smacked him them with the club and threw them in the pit/cage, could potentially be other survivors from the plane (tail). Or it could really be another group that was there before them, "The Others". At any rate, Jack's team has the guns now. They should be able to overtake this group, who seem to have primitive weapons.
4. Locke is breaking down psychologically, for him to yell "Jack, don't leave me alone!" as he left after Desmond is very unusual. He's normally the "Don't tell me what I can't do" and "I can take on the world alone" type. He was having those flashbacks of being conned by that man and having his kidney taken at the time. He seems fragile now.
5. We got another nice 2 second shot of Kate