One of the reasons I both love and hate writing: you have to not only know but understand so much. This means you should be perpetually in student mode (also sponge mode, as I am fond of calling it). You need to be always up on the current research in just about any field you think will impact your writing. And if you are writing SF and Fantasy, this better be everything from economics to physics to anthropology and back again. And it's not a bad idea to understand how we as a race of sentient beings interacting with this particular macroenvironment called Earth have gotten from "Ugh" to "I totally have to IM this Paris Hilton prison meltdown YouTube video to my entire flist." And so on.
As part of that continual learning, being on the lookout for folks shooting down the past romantic views of your genre tropes should be friggin' required learning for writers as well. One of the best such essays I've seen on the topic of space colonization is by SF author Charles Stross, and if you're considering writing a space opera or some other story in which humans conquer the Final Frontier, you best be reading this. It's an excellent summary of the obstacles keeping us firmly entrenched on Earth for the forseeable future with the exception of small exploratory forays. If your fictional space opera universe doesn't somehow explain away these concerns (and there are ways to do so, ranging from the scientifically valid to the plausible to the "now you're writing a fantasy" variety), then you might want to get back into worldbuilding. Just sayin'.