We are running vmware 5.1, using tsm for ve 6.4.2, and using nfs data stores.
It appears that change block tracking does not work with tsm for ve on nfs data 
stores.
This is forcing full backups every night.
Our environment is currently over 14 tB and growing.
With this limitation, we will not be able to continue using tsm for ve.

Have any on the list encountered this situation, and if so, have you found a 
work around?

Further information is here.
http://www-01.ibm.com/support/docview.wss?uid=swg21681916