A lot of people on the forums are complaining that they never see weather. A few people complain that they see weather too much. How about a control that lets you set weather frequency? You could select anything from "never" to "Seattle". And maybe an option to disable snow, since some people don't like snow.
I think the chances of weather depends on what biome you are in. (Not sure though.) Want more rain? Go to a rainforest. Want snow? Go to a taiga or tundra. Want little to no weather? Go to a desert or a savanna.
At least... I think thats how it works. I'm probably wrong. XD
I've been playing Beta 1.5 for many real-life hours, and I've only seen rain once, and that was in a new world. My main house in my regular world is in a forested area; no rain. I went to the tundra and melted a distinctive pattern in the snow. Many Minecraft days later, that pattern is still there, indicating that no snow has fallen in the interval. If there's a mod to adjust weather, I'll take it, but I'd like to see it be adjustable in the actual game, without mods.