Living in Seattle and hiking in the Washington Cascades and Olympics, I get a lot of rainy days. Two things to add to this thread:
1. After reading Ray Jardine's Pacific Crest Trail Hiker's Handbook, I started experimenting with an umbrella in the backcountry. One of the biggest joys of the umbrella is using it in camp to keep dry while cooking, bear bagging, middle-of-the-night toilet runs, etc. I also found it useful as an adjunct to a tarp to block off windblown rain at the foot or head of the tarp. Would really complement a bivy sack to keep rain from hitting your face. I think this addresses some of the questions presented in the comments.
On the trail, when rain is falling vertically rather than horizontally, I much prefer an umbrella plus a windshirt to any poncho or WB jacket. With brush or wind, though, it gets dicey.
2. I often cross-country ski in the rain (sick, I know, but I have a great time, really!). Snoqualmie Pass is only 1 hour from Seattle but it's only 3,000' elevation so it gets as much rain as snow. But here's the thing: although it's raining, the temperature is usually right around freezing, and you're surrounded by snow which chills the air, so it's about the worst possible conditions for hypothermia.
I used to wear GoreTex jacket and pants but it never worked well (too hot then too cold from perspiration). I finally settled on winter bicycling tights with a windproof WR front and stretchy super-breathable back of the legs.
The shocking breakthrough was just how incredible my Marmot DriClime windbreaker is! I can ski in the rain all day in that thing and be totally comfortable. Due to my ignorance and/or negligence, I have never re-treated its DWR, and it STILL works fantastically even though it totally wets out on the outside. I am just blown away. All I wear under it is a thin mid-weight merino wool shirt, with a sweater in my fanny pack for rest breaks. Somehow the DriClime moves moisture out so fast that it doesn't matter that the outside is barely even WR. Truly astounding.
BUT –and this is a big one– I would absolutely NOT be comfortable sitting around in camp with that thing on after hiking in it all day in the rain. Its exceptional performance XC skiing in rain seems to depend on my body heat from aerobic activity. So for rainy backpacking, while I would be happy to hike in the DriClime, I'd want to put on something waterPROOF and dry for sitting around in camp. Sometimes I think a non-breathable ultra-ultralight something-or-other for camp, such as a garbage bag with sleeves? 1oz? The next morning, put on the wet DriClime again and start hiking.