Personally, I do not believe that there is such a thing as too much knowledge as they asked today at Wizards.com. Which is why I have spent time researching such subjects as swan napkins, graveyards, and medieval sappers using pigs as incendiary devices. It certainly keeps my local librarian happy and busy!
Erin Evans suggests that you cannot pursue a college degree in "useless trivia" but, like so many writers, she admits to her fair share of silly knowledge. And I bet it comes in handy for her day job as Eberron editor. I also have to agree with Jenna Helland: there's nothing like a sextant! Especially if you plan to write nautical fiction.
Nevertheless, I will admit that my vast knowledge of weird science fiction/fantasy TV and even odder movies might be excessive. Give me dragons flying through the sky (Reign of Fire, Dragonslayer, and on and on) or dinosaurs AND wormholes (Primeval!!) or even strange adaptions of Arabian fairy tales (Tony Curtis and Piper Laurie, ahhhhh), I will be there. It doesn't even have to be the most recent stuff, as you can tell from the Tony Curtis reference. Black-and-white movies are just fine with me. Silent films -- especially if accompanied by live music -- are a treat. Almost every science fiction show with a British accent ( Dr. Who today and yesterday, and even the brief pilot on Fox) has passed through my DVD player. Tonight, I'm checking out Ink, a new independent film with a definite fantastical bent.