Mac OS X has been shipping with CIFs client support since version 10.1. To use
it, use the finder application' "Go" menu, "Connect To Server".
FYI, OS X also ships with a Samba and has samba management functions built into
OS preferences tools.
I've added a comment about the Mac OS X client to the download page.
I couldn't link to any additional info, as I couldn't find any. But
at least the client is mentioned with the others now.