Franco, you are right--if you are wearing a jacket or sweater and it starts raining, you'll sweat like a pig and have a wet jacket if you just put the rain jacket on over the insulating layer while you're hiking. I found it better to remove the insulating layer and stick it in a dry bag when I put on the rain gear. The dry jacket can then be put on under the rain gear to keep you warm at rest stops.

Last summer, during a 5-day backpack in Colorado, it rained almost constantly the first 3 days, with the addition of a series of thunderstorms starting about 5 pm. It was warm enough that I just wore a Capilene 2 top and my Campmor nylon covertible pants and got wet--I was less wet and a lot more comfortable than if I'd been steaming inside my rain gear. I put the rain jacket on for extra warmth at rest stops. Putting the wet clothing on in the morning was a bit challenging! I didn't do it until I was ready to start hiking, so my body warmed it up right away. At night, I changed into my base layer and wore the rain gear over it when I was outside. The 3rd day, fortunately, the sun came out at noon for several hours, so I stopped and dried everything out. About 6 pm, though, the daily thunderstorms showed up. The 4th day was clear and it froze that night. I certainly was glad to have everything dry before the frosty night!

I recently read a BPL article (another members-only article, unfortunately) about backpacking in long, cold rain. While this article had some useful ideas, there was nothing I hadn't already experienced. The article kept referencing New Zealand, even though it had a US author. The problem is that NZ has no bears. In bear country, you do NOT cook in your tent's vestibule and eat in your tent, as the article recommended! You'd think that, with BPL based in Montana, they'd mention this little problem. The article also omitted carrying a dry base layer. Evidently they wanted you to put a jacket on your torso and otherwise be naked inside the sleeping bag. Personally, I'd rather carry the extra weight of a base layer and keep the inside of my bag a bit cleaner. At least in the high Cascades and Rockies, after several days of rain, it will turn cold and often snow before it clears. When it does clear it will be well below freezing at night. In those conditions, a base layer is needed!