The theme of Islanded In A Stream Of Stars: having to leave things behind. Witness:
- Adama having to leave behind Galactica herself;
- Tigh having to leave behind the quaint fiction that he bears no responsibility towards the skin-jobs;
- Four different groups having to leave behind their dead in the vacuum of space (loved that funeral scene);
- Kara having to leave behind Starbuck; 
- Boomer having to leave behind being happy over anything ever again;
- Helo at least thinking he has to leave behind his child, and probably his marriage, too;
- Roslin having to leave behind her life and her home;
- Galen having to leave behind showing up in the fucking show, as part of the more general problem of the writers having to leave behind explaining what the fuck keeps happening to anyone who does naughty things;
- Galactica as a show having to leave behind being even remotely subtle, as oppose to just beating you about the head like a lunatic old man with a paintbrush, shouting SOON WE WILL BE GONE AND YOU WILL MISS US.
I really don't have anything more to say. This was obviously another episode of jostling for position before the charge, a sufferer of the exact same malady which afflicted the first half of the season, and once again a reminder of the irony that so many whined that Season 3.5 was insufficiently arc-based.
Should Daybreak kick enough ass, this episode will probably come to be seen as a pause for reflection, the selah that separates Ellen's revelations from the end of the journey. It's entirely possible, and serialised (or semi-serialised) TV series often work better as complete works then they do episode by episode. I've said before that set-ups like this live or die on the quality of their pay-offs.
Of course, the last time I said that, I was talking about Matrix: Reloaded, so I'm pretty skeptical right now.
 Oh, and wow, is she stupid. Telling Baltar she's a zombie? He's either a religious nut, which she doesn't believe anyway, and thus liable to pull some stupid-ass stunt with what he knows, or he's still the same crazy, selfish weasel he always was, and will thus pull some stupid-ass stunt with what he knows. I guess I should be willing to forgive her, though, since a) it's totally in her nature to knock all the pieces over in the hope something good happens, and b) at least she was trying to move the plot along instead of whinging.