I just put a Brooks B-17 on my commuter bike. It is not yet broken in and at this point is about as comfortable as the cheapo saddle it replaced (not very). I gave it a good baptism in neatsfoot oil, so hopefully I will start seeing the benefit of a leather saddle in a few hundred miles.

The B17 weighed in at 1.2 lbs after being soaked in oil. The plastic saddle it replaced was 0.8 lbs. Not that big a deal.