The Truth About World-Building
I recently read a somewhat old post about world building from the Tales of the Grotesque and Dungeonesque blog. I've talked in the past about simplifying world presentation, and the post really resonated with me. Years ago, I definitely was the type of DM who wanted to detail his world to the nth degree (though generally after I over-detailed something I would get tired of it and move on to something new - tells you something about doing that which I didn't catch onto for too long...). But I've seen that, in general, your players really don't care about that sort of thing. Heck, when I'm a player I rarely care about that much detail.
Which is the point that the post above makes, among other things. World-building is a fun activity, and if you want to go into hyper-detail mode, go nuts. But don't think you're doing it for anyone other than yourself.
Now, that's not to say that you shouldn't flesh out anything in your world or just drop it for a pre-published settings, just keep in mind that extensive detail should be reserved for things that will actually enter play.
On a side note, the Tales... blog is overall a good one and worth checking out. Take a look especially at his "World Between" PDFs. Really good stuff - enough information to spark your imagination but not so much you're swimming in details you'll simply ignore (I stole some of his presentation technique of the regions/kingdoms of the "World Between" for the most recent Mythosa PDFs).