For anyone interested...
I got mine at release and have been using it heavily for the last week.
Battery life is good - 8-10 hours depending on how often I play Hearthstone.
With the keyboard down, ease of use is excellent. I don't really understand why people can't seem to use the SP3 on their laps. The S3 is comfortable in every situation: on a table, on my lap in front of the telly, in bed resting against my knees, whatever. The three-position stand covers every eventuality. Very impressed, and I was concerned about this based on some previews I'd read.
As a tab it's heavier than the iPad, but I don't really trust myself to compare ease of use because I really don't like iOS at all. However, based on my experience, it works okay in tablet mode, and everything about the touch surface is excellent. The OSK is good, and Win8.1 in touch mode is excellent (lack of apps notwithstanding etc. etc.). For me, though, when it comes to tablets, anything bigger than, say, the Nexus 7 is not worth buying for the tablet experience alone. The beauty of S3 is that you get a good tablet and an excellent laptop.
And as a laptop it is excellent. Again, I was worried about the type cover but the keyboard, while small (which takes some getting used to), feels good under-finger and with the back-light looks terrific. The trackpad, which again has received some criticism, is small but otherwise fine. I've done a lot of writing on this thing over the past few days and it's a pleasure to use.
As a device, it looks fab. It's positioned between tab and laptop and the size reflects that. Build quality is exceptional. It's also an attention grabber, if you like that kind of thing.
One thing you can't get away from is the price. You get more than an iPad, but you pay way more than an iPad. I bought a bundle from PCWorld and got S3+type cover for £525. That's a freaking lot of money, and nothing I would ever have paid usually except that the device is powerful, unusual, and I'm bought-in on the MS ecosystem so it slots into everything I do for home and work with only five minutes' setup. So, a luxury purchase, sure, but not one I regret.