I am asking on behalf of someone I know that is looking for these products.
Added (1). From what I understand, Nikon has not specifically commented on this problem, but many users are reporting oil splatter on the sensor and excessive dust.
Here are some web reports:
http://nikonrumors.com/2012/11/29/the-oil-spots-on-the-nikon-d600-sensor-seems-to-disappear-after-3000-shots.aspx/
http://forums.dpreview.com/forums/post/50119071
http://www.petapixel.com/2012/11/21/a-time-lapse-showing-how-quickly-dust-accumulates-on-nikon-d600-sensors/
>>> I am hearing of spotting problems with Nikon D600. Does this problem exist on the D800?