ShadowSun notes that he is surprised how few opponents surprised how few opponents build a second library

Building a second libary is really cheap, and good insurance in case your primary is destroyed or captured. You can also research 2 techs at once, which can be nice in some situations. For those of us who can't multi-task well, you can get behind in research when you're focusing on a large battle. Two libraries can help you recover from that mistake.

In the thread, I note out that I have never built a second library. IMO, it's not really necessary. There's not much research that can occur simultaneously. People get behind in technology due to poor economy, not because they only have one library. On the other hand, it is pretty cheap and if you've got an idle villager later in the game and a second library would make you feel better, go for it.
posted by Tim at 6:01 AM