http://www.nikonchat.com/nikon-apple-software/

Why is the Nikon D90 camera is not able to download images to a computer?
Data transfer The D90 has a design flaw: when connected to a computer, does not always appear directly as a hard drive, like other Nikon cameras do. There is no USB menu option for PTP or mass storage. PTP is stuck in s, that is, if you want to connect the D90 to your computer, you will need certain software or operating systems to recognize it. works While in some teams, but does not work unless I futz with my own software, I will not do. You may have to buy a SD card reader separately, or opt to install buggy software on your computer Nikon always download directly from the D90 if Apple's Image Capture or other software does it for you.
I use a USB 2 card reader, saves wear on your camera are so precious and cheap, mine cost less than £ 10.00, why use anything else? The new SDHC cards can be used as well. I've seen USB2 SDHC card reader £ 1.00 in computer science fairs. Chris
The Geekinator #0302 – ipad, NASA, Nikon, and Google Nexus One