It feels like the right time for the writers to deliver a few advancements to subplots, so this transitional episode fits the typical design. The difference is that the story is tied together with questions of identity and the dependency of machines. Thematic episodes are often fun, because it gives the audience a glimpse into the depth of the writers' room.
Cameron's origins are revealed, and as expected, her model is based on someone close to John Connor. Allison Young was, at the very least, a member of John's cell, which means there was a solid basis of trust. The terminators attempted to exploit that trust with an infiltrator model, which explains why Cameron seems more adaptive than the typical terminator.
But the implications are a bit more complicated. John obviously has a close relationship (and attraction) to Cameron in the "present". Within a generation or less, John will meet the real Allison Young and it's hard to imagine that he wouldn't recognize her. Does John therefore make the connection, knowing that Cameron will eventually replace Allison, and does that prepare him for the moment of her "betrayal", giving him the chance to reprogram her and send her to the past? (Another thought: was Cameron channeling Allison when he was telling John that she loved him in the premiere?)
There's also a possible connection to the first season episode "Dungeons and Dragons". Derek wound up captured by terminators and held in a bizarre facility where something strange was being done to the captives. Could that operation have been similar to what happened with Allison and Cameron in this episode? If we hadn't already seen Derek with some severe yet very human wounds, I might even suspect he was a terminator.
But the fact remains that this is Cameron's second glitch since the premiere, and while it may not have been immediately dangerous to John, there's little doubt that it was a serious problem. John should say something to his mother and Derek about it, but it's also clear that his judgment is less than stellar when it comes to Cameron. At the very least, she should be volunteering to have her chip repaired, or John should be insisting on it.
Exploring the similar theme of machine malfunction and identity, Agent Ellison decides to accept the job with Catherine Weaver. Weaver seems to be designed closer to Cameron's "infiltrator" mold, though obviously a more advanced model, capable of emulating human behavior better than the average terminator. I'm not sure about her goals yet, though I suspect it is tied to Cromartie's decision to let Ellison live. If nothing else, this episode did much to flesh out Ellison's character, which was good to see.
There was some exploration of Sarah's psychology in the final subplot, but it was mired in a tedious pregnancy drama. I can't be the only one who doesn't give a damn about Landlady. The only interesting point was that Trevor is a cop, which presents Sarah with slight situation. He could be a potential ally or a serious impediment, depending on when the inevitable violence occurs.
Summer Glau made this episode, and she's currently blowing the rest of the cast out of the water. I'd like to see the writers give the rest of the cast such powerful material. In particular, Lena Headey needs to get more consistent material as Sarah Connor, because right now, the title character is not quite deserving the focus. Hopefully, despite the falling ratings, the series will last long enough for the season and cast to gel more completely.