Hmm, haven't really given it that much thought to be honest

Just noticed that it doesn't fill up my entire screen

But the option to widen each column would be nice, preferably letting the user choose the width, if possible. In history the column for the save path can sometimes be a bit to narrow in my opinion. Other than that I can't really think of anything specific right now, I'll think about it over the next few days. See if I can come up with something useful.
Edit: Maybe a column that displays from which nzb site I've downloaded the .nzb? Dunno if that's something that interests the crowd though.
Edit2: A column that would contribute, in my book, would be a 'category' column, and maybe age? For all these I personally believe they'd benefit from being opt-in/opt-out options - for wide screen resolutions.