While the thread is giving others useful info, I would like to add some focus to my particular situation. I live in Las Vegas.
When I'm on serious snow, I take one or two pairs of serious glove/mittens.
However, I also always carry an emergency pair of light gloves, summer and winter, for windy/cold days that may be more like 25F to 45F; and then I rarely wear them for more than 15 minutes at a time. In these circumstances, I'm often burning a lot of calories in my legs and torso, but my hands are exposed; I may be wearing shorts at the same times as I wear such gloves. With luck, I just need to pull my hands out of the sleeve ends for occasional touches to rock or old snow.
I try to keep the gloves small enough that they will fit in the small pockets on my hooded windshirt and lightweight eVent jacket. In fact, I leave a pair in each garment, along with a lightweight earband or balaclava.
Since it is usually fairly dry out here, I used old polypro glove liners for years. But for some uses, these liners wet through very quickly -- e.g. when I was caught in a very sudden late-spring graupel storm at 11500'.
I looked at several options at REI, and noted some touted semi-waterproof membranes, thin fiberfill, and so on. The Serius hyperlight was among them; however the
reviews were mixed. I'm not sure if the reviewers just had unrealistic expectations, or comments like "they never dry out" should be taken seriously.
Thanks.