Yep, humidity can cause circuit board corrosion. And as mentioned, dirt, dust and grit is another issue. This article mentions open windows:
http://www.threadsmagazine.com/item/...nance/page/all. If humidity isn't a problem, just tossing a cover over it for the evening can help. I have to do that anyways because of the furry ones lol. You can even make a really cool one yourself (I bought a personalized one because I had just started and wasn't at that level yet!)