v1 is still available for download, but has officially been depreciated. v2 is in the works.
Nike+PHP v1 down
It looks as though Nike have removed their support for v1 of the API. Although I have been working on v2 of the API, I am not even close to being able to release anything yet.
I will update the site when I get some time to work on v2, but for now, it looks like Nike+PHP is unusable.