Hi Johan,
For SAN I read something like a fibrechannel connected replacement for an EMC array, for NAS I read an Ethernet connected replacement for a NetApp array.
SAN doesn't seem to be something well supported on FreeBSD, relative to Linux or Solaris for example.
At different levels I think there are many success for NAS, as iSCSI, NFS and CIFS. Although NFS on ZFS has some performance issues relative to UFS.
cheers Andy.