<p>Yes, I've used the camera SDKs. There is an application you need to complete before being allowed to download an SDK, but nothing prevents individuals from going through the vetting process. The time from submitting an application to receiving the download link is a matter of minutes.<br>
The SDKs are reasonably well documented and complete. However, the native Nikon MAID interface is at a fairly low-level, so many of us choose to employ Thomas Dideriksen's wrapper (offered for free at SourceForge). The wrapper supports C# and VB, is well maintained and easy to use. Note that if you elect to use the SDK wrapper, you will still need to download the SDK for your camera in order to access one of the binary files included with the Nikon distribution. </p>