jabber.el supports a subset of XEP-0050, the standard for Ad-Hoc Commands. As the name implies, this can be used for just about anything. It has been used for remote-controlling clients (e.g. Psi), and administering services (e.g. PyMSNt).
Currently, jabber.el uses ad-hoc commands for setting presence remotely. If you realize that you forgot to set your client to “away” with a low priority, you can do it remotely.1
The commands for executing ad-hoc commands are available under the Service menu, which is opened by typing C-c C-s.
To find which commands are available, run “Request command-list”
(jabber-ahc-get-list).2
To run a command from the list, put point over it and run “Execute
command” (jabber-ahc-execute-command), accepting the defaults
for JID and node. (If you already know those, you could of course
enter them yourself) The form you get should hopefully be
self-explanatory.