Unfortunately I am something of an expert in rain hiking. It's not something I'm proud of, but most of my hiking is done in the coastal rainforests of vancouver island. I've been on 5 day hikes where it rained for 6 days. Now I'm getting a bit older I try to avoid the wettest seasons, but I love the scenery so much I just can't stay away for long.

If you're on a hike where the rain is most likely going to end within a day, I think it makes sense to try to stay dry, put up a tarp or umbrella, wear your "waterproof breathables", etc. If the rain looks like it will continue for several days, I think you're better off to just immerse yourself in it. Trying to hike in anything waterproof will just get you soaked from sweat, no matter how breathable the clothing claims to be. Get wet. Walk through streams. Jump in the puddles. Just keep moving and stay warm. When you get to camp, set up your tent and get into your warm dry clothes. Hopefully you have somewhere dry to cook, make yourself a hot meal and hot drink. As long as you keep warm, you're safe. The next morning you might have to put on some wet clothes, which is awful for the first 10 minutes, but you soon get over it.

Other tips when hiking in potentially heavy rain areas:
-bring a small ultralight tarp or tyvek sheet and string, having a dry place to cook and relax is wonderful.
-bring extra hot chocolate, tea, coffee, whatever your vice
-package each item in your pack in a waterproof bag. No matter how dry you keep your backpack, you'll need to put wet items inside which will transfer to your sleeping bag.
-It is possible to keep a down bag dry, you just have to be careful.
-Bring a book or something to do if you're forced to spend a lot of time in your tent.
-Hike longer miles, do some side trips, keep moving and stay warm
-Burn your goretex, it'll keep you warm for a while that way.