As an admin, I really miss Net Send. I would love to have a simple way to send messages to users, especially in an emergency (like the office internet going out) so I don't get told 20 times.
It sucks that they depreciated it. I wish it were still around, maybe we could have it disabled by default, and just use a GPO to enable it.
If I need to get a message to a machine or troll someone, I do a psexec -s cmd to their box, then do:
msg * "insert message here"