Heh, true.  Are 0 input/output transactions actually valid.  I thought at least 1 input and 1 output was mandatory (or 0 inputs for coinbase).  You can have 0 valued outputs though.

Have any actually ended up in the block chain?

2: Malwritten clients, when served with a amount to send = 0 BTC by the end user (propably by mistake, user simply forgot to enter amount), do not validate that the clients amount exceed 0 Before attempting to create a transaction. When the client attempt to create the transaction, it finds out that theres no need for inputs anymore ("do until"-loop) because the amount has been fulfilled. And theres no outputs to add, because the client automatically deletes any outputs with amount=0.
Then it ends up with a "empty" transaction, and sends the "empty" transaction.