I've been writing ljupdate.el, the Emacs client. It rules. :)
Currently, it works under GNU Emacs 20.x and some of the 21 pretests. If anyone's interested in porting the code to XEmacs, be my guest. It would be cool if ljupdate worked under both, but I don't know much about how XEmacs differs to do the port myself.
Here's a shot of ljupdate in an xterm under 21.0.104:
Right. So anyway, that's about it for an intro, I suppose.