A quick check of our LDAP directory indicates we've got about 500 accounts, a good portion wont be particularly active, however some users have two partitions. The partitions are unequally divided between 4 servers, and vary in size from a few GB to about 1TB. For this ZFS seems to work fine, although I would love to improve throughput NFS + 1G ethernet results in awful lockups every now and again, and we only have about 16 NFS clients.
I don't envy you with 30k+ users! I hope there is more than one of you, I have to make sure I check both ways when crossing one way streets and my boss grumbles whenever I mention the word "holiday".