Model: 38mm Sport Silver
Day length: 15.5 hours
Watch battery remaining: 47%
iPhone 6 battery remaining: 51%
38mm Sport went on at 0930 this morning, and I just removed it at 0100.
Usage for the day included showing it off to various family members i.e. demonstrating the various functions, numerous email/text notifications, plenty of activity (~11,000 steps), and occasional checkins with maps/weather/Twitter.
The phone battery is usually a lot less reduced than this, but I spent a lot of time on it today checking up on things while I was out and about, so it doesn't surprise me.
Overall, I am very, very happy with the battery life so far. I have no issue with nightly recharging, and as yet I haven't needed to top it up at any time beyond that.