While working on a project I noticed the new "sendrawtx" command and figured it would save me some trouble.
Long story short, I've tried sending many well-formed valid transactions through this command, none of which were ever broadcast to rest of the network, even though they were accepted and the txid was returned by "sendrawtx."
The command seems to correctly verify that the inputs are valid and that the transaction otherwise meets the requirements of the network, however it does not appear to ever relay it to it's peers.
Edit: I note also that the transactions I tried end up in that client's "getmemorypool", but not in any other clients, even when they're directly connected with -addnode.