Here’s a blog post by a guy at Sun which goes into very deep detail on what happens when a read() is done against a file on an NFS filesystem. Amongst other things it explains, why we see GETATTR’s turn up at the NFS server, even when the attributes should be cached locally (the answer is that a GETATTR is performed at file open() time regardless of the timeouts on the attribute cache) There is a 40 page PDF document linked to the post.
http://blogs.sun.com/vallishguru/entry/solaris_kernel_nfs_client_s