Expect everyone to get an hour and a half first day while they constantly play with it. I managed to burn out my 6+ battery the Saturday after delivery
I got mine on launch (42mm SG Sport). No issues with the battery whatsoever. I am using it a lot including daily workouts and plenty of notifications. It goes on about 8am, off about 12-1am and is usually around 30% remaining.
Mine came off the charger at 6:30. Did an hour spin class with it, and have been using it fairly frequently today - checking calendar and activity and answering texts with dictation (and showing it off a bit) Now at 2:00 I'm at 60%. Not bad.
The battery life on the Watch and my iPhone6 have had the effect I hoped for so far, offloading some activity from the iPhone to the Watch I can get through a full day with no worries on either.
I take both off chargers at 5am. 11 hours later both have 70% charge (today has been a light day). The past few days were heavier usage and both had 50-60%, which is more than fine for me to make it til very late at night.
I got 39 hours out of mine before it went to power reserve with moderate usage (some navigation, music, apps etc.). Worth noting I have default brightness and prominent haptics on, a 38mm model, and have NOT used the workout app.
The first day I used the butterfly interface and I got 6 hours on a battery. Switched to modular and yesterday was 13 hours 33 minutes standby and 3 hours 17 minutes usage. Battery was about 33%.