For many of us. the purpose of rain jackets is to keep us warm when wet, not to keep us dry. Avoiding hypothermia is the goal. In short rain storms, I may be able to stay dry as well. Unless I'm not exerting myself, I'm going to sweat under my jacket, no matter how "breathable" it is.
For me on the AT, it boils down to getting wet and sweaty in 45-minutes wearing a waterproof breathable jacket or getting wet and sweaty in 20-minutes wearing a non-breathable jacket. I'm going to be walking for 8-hours a day. If I can get a good lightweight jacket that doesn't breath well for $40 at Dick's or spend hundreds on a Gore-tex jacket, is the extra money for an extra 20-minutes of breathablilty worth it?
I have a page with rain gear options and material options on my web site at: http://friends.backcountry.net/m_factor/raingear.html
It hasn't yet been updated to include Cuben Fiber. Pros: lgihtweight; Cos: durability may be an issue.
Packa comment: I like the Packa but found that unless I'm someplace with shelter, I needed an extra pack cover anyway. either that, or I got wet if I wanted to keep the pack dry.