The one I got the N-918/N1 has the 10pin connector (moulded to the GPS unit) so if your camera has the 10pin connector for the GPS then it should work - looking at the listing on mine
(Youngnuo N-918/N1) it works with the D700, D300, D300s D2X D2XS D2HS - IIRCthe D90 has a usb type connection in the side of the body as where as others (as stated) have the 10pin connector...
Works just as good as the Nikon GP-1 but with out the cost that additional cost that goes with it.... Althou with this one you DONT get the strap adapter, D90 lead, nor a manual or a Nikon box - then again the GP-1 costs £190+ compared to a very similar looking GPS @ £60 delivered...