It should be, with an original receipt, as long as you are willing to impersonate (!) or as long as the camera hasn't been registered to the original owner, if you are not willing to impersonate. My local store doesn't put the buyer's name on the receipt, so no one would know who bought it.
If your maneuvers are discovered, however, I imagine the warranty would be toast.
As for the camera itself....I'm still deciding whether I like it, after four months and maybe 2000 images. There is much about it to like: ergonomics are great; lenses excellent to spectacular (I jumped in with both feet, buying the camera, the grip, and the 14-24, 24-70, and 70-200 on two credit card cycles ); color rendition and color tonality, very good. AF is quite good once you get the hang of the welter of modes and settings. Took me a while. For general use, for sports, wildlife, etc, it's a great camera.
I guess I'm just an unrepentant B&W film shooter; I shoot a lot of B&W, and it just doesn't make it for me. There is just something missing from digital B&W that is just obvious when viewing next to a film image. [Please, no flame wars or chest puffing--it's just one man's opinion, everyone.] Can't say that this is specific to the D300, as I wasn't blown away by the B&W conversions from my Kodak ProBack--which despite its quirks is a really first-rate imaging device--either. Perhaps it's the DX-format chip; and I need merely to drop another $3k for the D3 and its FF chip; or spring for whatever Nikon has coming next at 24+ MP. Or maybe I'm feeling the post-Mastercard letdown--the hype around the D3/D300 has been so over the top that maybe no device could ever measure up to that. Or it could be that, for what I most like to do (B&W portraiture), the D300 is just not the right tool for the job.
I shoot RAW 100% of the time. I find that noise is acceptable to about ISO 800 in daytime; strangely, shooting at night, higher ISO's are acceptable--even 3200 looks pretty good in a way it would not look in daylight. Guess that's because there's more actual stuff visible in daytime shots, in which to pixel peep and obsess over noise.
I've had no occasion to delve into Live Histogram, so I can't speak to that question.
Hope this highly subjective, stream-of-consciousness mini-review is of some help.
