NFS user space vs. Kernel space daeomn?

I am aware of at least one difference in behavior between the userspace NFS package (nfs-server-2.2beta51-209) , and the kernel space version (nfs-utils-1.0.7-3). Experimentation indicates that the user space version supports the sharing of a dvd (by exporting the parent directory /media). I recall in years gone by there were certain automounting functions that only worked with the user space package, but I have not recently reproduced that behavior. Unless, of course the dvd sharing is actually a result of the same behavior. Can anyone say what the advantaged and disadvantages of each of the NFS server packages is in comparison to the other? -- Regards, Steven