When you're outside and it's dark, it seems dark but we also have enough ambient light such that you can find your way around. To me, weather effects, whether it's rain and snow or simply time of day, should ADD to the immersion of the game and not turn into an annoyance. I don't want players bemoaning that it's getting dark because it makes their gameplay experience less enjoyable.
I also want to see weather really matter and not simply be a cool effect to which you say 'wow' the first 3 times but then afterwards bemoan it as well. As I've posted in the past, we have the capability of making it such that spells and other abilities work better, worse, differently, etc. based on time of day, weather, and even what day in the Telon calendar it is. I'm really excited about this because it adds some variability to the world.
Lastly, I do want to say that dungeons and other crazy places are different. There are places that should be dark -- very dark. Torches, light spells, etc. should be part of adventuring in the depths. But outside... not so much.
Source: Aradune Mithara