I think the destruction of The Swan is going to reveal something entirely new to fuck with Locke (and possibly Eko). One of the producers made a comment recently about how they've torn down the entire hatch set and rebuilt it as something completely different. Also, when Sayid and Jack are down in the pipes early in the season (God that sounded gay) Sayid mentions something about the blast doors protecting something.
I was watching the bonus disc and they talk to L. Scott Caldwell (Rose) about her episode with Bernard and how it stems from L. Scott meeting her husband during the filming of season one, only for him to be diagnosed with end-stage cancer shortly after. They married and he died a few months later. S.O.S is all the more of an awesome episode for it and, IMO, one of the most underrated ones in Lost history.