I have seen charts and graphs that actually do point out that turnout is lower in inclement weather. I’m lazy and I am not going to dig them up for you.
The weather thing would probably benefit Obama. People are excited to vote for him and will put up with more to cast their vote. The McCain crowd isn’t as enthusiastic.
edit :: And to answer your question. I have already voted. And if I hadn’t I would happily stand in the rain for a few hours tomorrow.
No early voting in Maryland, so I imagine the polls will be crowded. It is worth any time or trouble to be able to cast my vote! I wouldn’t miss it for the world!