buy this lens new (unless you can save at least $150) and adorama is a fine place to get it
for a $75-100 savings over used you get 5yrs of warranty
the prob with used is alot of us payed too much for this new so we want to get too much for it used....$510 for a mint copy would be worth buying used (and ask for the original receipt and warranty card)
I recommend buying new also, for the following reason: I bought one new in December, '05, when they were first released. It has been used extensively since, and on our recent trip to Spain, the front element became very loose. As soon as we returned I sent it back to Nikon. They fixed it under warranty and returned it promptly.
On that same trip my 35 f/2 that I had purchased used from B&H developed a problem in not communicating the aperture setting to the camera. It went to Nikon in the same shipment, but they kept it six weeks and charged me $119 plus shipping to fix it.
So I'm sure it's worth a bit extra to get the warranty, and your price sounds pretty good; it's about $100 less than I paid in '05.
I like Adorama but I like Amazon too because of their no nonsense exchange policy.
As long as you buy a lens sold by Amazon you can return it or exchange it for free for at least 30 days and they pay shipping both ways. Get a lens that you don't like for any reason and you want another copy...just fill out the online return request and they usually next or two day you a replacement and supply you with the return label.
Then, once you own it, watch the price on Amazon for the next 30-60 days and shoot them an email each time it drops and they'll give you a refund of the difference.
Lastly, get an Amazon credit card and your first purchase is $30 off. You will earn 3 points for every dollar spent on products sold by Amazon and 1 point for every other dollar. Then every $833 you spend (heh, one lens) you get a $25 voucher. Just be sure to pay the card so you never get charged interest.