I've used my Touch in the rain and unprotected. Here's the thing: the rain won't hurt it unless it gets deep inside the case. If it's raining hard enough for water to seep inside, the screen will end up being obscured by raindrops anyhow. So you couldn't read even with a cover.

Water inside these devices is also easy to deal with. Remove all power sources and let it dry completely. Yes, that includes removing the battery. The reason is that water doesn't damage the electronics, electricity does. Water simply provides a way for electricity to go where it isn't supposed to. When the water is gone, everything returns to normal -- assuming nothing was damaged when the circuits were powered.