I've had a GNex since last November & here are my answers:
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Sucks, I'm a pretty heavy User though but I get about 6-8hrs from full charge-0%. As such, I never leave home without my backup battery (both are standard 1,750's) so that way I easily get through the day, but still.
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2. How fragile is this phone?
Some say very but mine is always naked sharing pocket-space with my money & is more or less fine. Sure, the outer rim where the glass meets the plastic has a few nicks but the screen is perfect.
The only part that has a slight cosmetic scratch is right under the LED indicator but that's from when I tripped on rough cement steps slamming it screen-down & it scraping the cement to break my fall. So considering that's the only damage, I'm very satisfied.
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3. How well does it work with ATT service?
I'm currently in Canada but I've used it on AT&T, T-Mobile & a few other international carriers & never had a problem.
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4. Is there anywhere to buy more samsung accessories than the Nexus website has?
I couldn't find any actual stores - had to order mine online from another carrier's website.
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5. General thoughts on the phone itself?
Overall I love it. I've had all of the Nexus phones so maybe preferential to them, though I've had non-Nexus too (Optimus One, Galaxy Ace, Galaxy S2, One S)...but IMO there's nothing like a Nexus.
My only real complaint is the battery so hopefully they improve that in the Nexus 4 when I get that in a couple months, which I would personally recommend you wait to do instead of getting the GNex.