Very quick comment, it's not a major flaw or anything, but I've heard (and I agree) that white-on black is painful on the eyes, try light-grey on black (like #eee) for the columns on the sides, otherwise, looks good.
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Edit:
I guess the cramped look is what you are going for if it's classifeds, but in my opinion (take it with a grain of salt, I'm too often a reliable source, but hey) the cramped center and packed black columns contrast too much with the white borders (widescreen monitor). It looks like all your content is cramped in the middle. If that's not what you're looking for, try either taking advantage of the whole width available, maybe using a PHP generated stylesheet and some calculations from screen width, or something like that, OR making the columns blend better with the padding (say, if it was on a white background or something)
I haven't considered how that would actually look, so it may be hard to implement without jeopardizing the look.
Besides, the functionality is probably a lot more important for what you are trying to do, so a non-ressource-intensive, super-simple look might be what you want.