Lost: Of course there's poison gas

I'm enjoying my third go around with season 4 in Lost, in part because I don't remember these episodes very well. My gist of the season was that they would leave the island during this season, but beyond that there were some big holes in my memory and my understanding of the season.
In particular I was a little unclear about the episode called, The Other Woman. It revolves around Juliet's backstory, which is interesting by itself, but also hints at the fact she won't have a future. Literally just came up with that right now. Everyone else gets a flash forward, if they're making it off the island. I should have known then!
Anyway, the back story isn't that interesting, but the events in real time are quite confusing. WEll maybe not confusing, but at the time I remember not caring for the episode. Now I'm not sure how I feel.
The episode primarily deals with Charlotte and Daniel's attempt to turn the poisonous gas inert. This is the poisonous gas that most likely killed everyone in the Dharma initiative.
First we need to wonder how they knew about it? At this point we're left in the dark, but I assume it Charles Widmore warned them about it.
There are a myriad of other questions and complaints, but they're all trying to escape at once and I don't think i'll be able to articulate my frustration. The episode just feels like a throwaway episode I guess. The plot isn't well explained, and it's not like there is some big payoff later on that they were setting us up for.
So I guess, eh. Whatever. It just sucks to waste an episode in a season that was shortened because of the strike. Although, I kind of wonder if there would have been more time fillers if the strike hadn't happened.
We'll leave you with this hot, but not relevant picture.