I recently converted my Time Machine backup to use NFS instead of Samba. All in all, it was a pretty simple procedure. By using NFS, I dropped userspace CPU usage from a maximum of 40% with Samba to no more than 7-8% with NFS. This is on an AMD 4800+ X2, so the performance gains will be even bigger on slower machines. This means that my media server can now play HDTV h264 files without lagging during backups - a huge win for the elusive "WAF"!