I am old-fashioned, I suppose, in terms of a "Be Prepared" mentality based in having been in hard weather or other situations and so I try to balance wisdom with lightweight. Wisdom and a predilection for an old pack.
So, I use "waterproof" silnylon stuff sacks for my down bag, my down puffy and my "ditty bag". I carry my other clothing pressed flat in slippery, clear gallon ziplocks that keep dry clothes dry and wet clothes from affecting the rest of the pack and then utilize a trash-compactor bag and construction string for my pack cover in rain. My pack has been sprayed with a silicone analog to Scotch-Guard, and it beads water if wet.
A liner-bag doesn't work well for my system, because my pack has six distinct compartments, but the tried-and-true systemic approach to gear management has kept my gear dry in extended rains, after a dropped pack in the river that resulted in what must have been 80 plus lbs of weight to pull out of the water when I got to it and in fair weather where the simple organization and ability to press-out air from clothes makes for easy packing, finding and moving of gear from pack to tent, etc...
In terms of the stuff sacks, I think those E-Vent bottomed sacks are super cool and have been lusting for them, but I've been satisfied with the Sea-To-Summit silnylon bags which are available in different volumes for jackets, bags and etc... For the small stuff, the "waterproof nylon" bags sold in the 3-pack at Walmart for ten bucks have been great. 3 sizes and colors in one pack, with roll-tops.