Hey Derek, I guess it really depends on how hard it is raining and what you would consider to be hard rain/storm. I'm a pretty tall guy so I need the bivy to keep dry if the storm is really rolling in. You'd be fine for light rain but if it's coming down hard, the rain splash will eventually get you. For comparison, even with my Duomid, I have to move my pad and bag as close to the center as I can when it is really pouring or it will splash under the sides, even if it's pitched just a few inches off the ground.
I guess you would expect the sides of the bivy to get some splash on it, but that's what it's designed for.
David, it weighs 4.1 oz with the guylines.
Doug, good eye, it was heaven. That was from last weekends "beer"packing trip - I'll post a trip report soon.