>I have some questions. Is there a >difference in quality between the two?
They are identical. The lenses are made in the same factory by the same people with the same parts. The Nikon USA version is imported by Nikon USA the official importer. The Gray market lens is imported by someone other than Nikon USA.
Lenses imported by Nikon USA include a 1 year international warranty + a 4 year extended warranty. Gray market lenses ussually include a 1 year warranty provided by the retailer. Nikon USA Service will not service a gray market lens even for a fee. As Anthony wrote above, Nikon Authorized Service Stations will service gray market lenses.
>Why do I see the same >lens on eBay used for more money than the new one?
There is no logic to the prices found on flea-bay.
>Is there a >reliable place to get a good deal on used lenses online?
www.keh.com Also both Adorama and B & H sell used equipment as well. All stand behind the used gear that they sell and provide warranties. Good Luck and Enjoy your Nikons!