Lower Manhattan just had one hell of a thunderstorm cell roll through as I was getting my overpriced lunch, and the thought came to me - I pretty much leave weather out of my campaigns unless it's part of the plot or theme. I don't really put rain / snow / wind / heat waves and the like into the game as window / campaign dressing.
That might be a failure on my point, but I suspect if I added it now, the players would suspect the weather to be a plot device that it isn't. Actually, maybe that would be fun anyway, as some of them see plots devices in the dark that I never planted in the first place.
What about you?
Do you use weather in your campaigns as part of the back drop, as a plot device, or not at all?