Voted down because I don't believe your claims about SMB being too slow and NFS being too hard. If we're looking for interoperability, then we've got to support SMB, it's that simple.
NFS3 is insecure (uses host-based authentication). NFS4 _can_ be secured, but you need a real expert (enterprise admin type) to do it -- or 1000 inexperienced users typing at random.
SMB is somewhat secure in that it requires a user/password. The trouble is that there is no "share this folder" functionality in Linux. Also, Samba is primarily used as a Linux server and Windows client. Using it Linux-to-Linux is farther off the beaten path, so you are more likely to encounter some obscure bug that nobody knows about.
The entire process (security, GUI tools, bug-free) needs to work for at least one flavor of file sharing, and preferably for more than one!
Easy file sharing in Linux is a complete mess ATM.
NFS shares are not browsable, samba is not easy neither - there ie no easy option to simply say "share this file with anyone" - and it WORKS.
BTW, this is a dupe of http://brainstorm.ubuntu.com/idea/403/