I still remember the first time I got excited about a TPE.  It was when we traded Antoine Walker to Miami, and we created a TPE for slightly over the MLE.  The talk was that we'd have an advantage in free agency because we could offer more than other teams (via a S&T).
That one wasn't used, either.  It's been a long train of wasted TPEs ever since, with some exceptions.  (We used the TPE created in the Pierce/KG trade to pick up a #1.  Did we use a TPE to absorb Brian Grant in the deal to draft Rondo?