One of my clients has the 4S (5oz) with the Mophie Juice Case (3oz). I was holding its 8oz beastly features, and hike not was light, it was nice to have something that substantial in the hand.
If you've handled a lightweight phone for ages the Lumia would feel heavy.
If you've handled a heavyweight phone for ages, the Lumia will be nothing and everything else feels too damn light. Almost to the point that you'll forget you're holding it and/or you could feel like you could snap it in half.