SlideML is great. If you followed this blog a bit, you know I'm writing all my presentations with it, in order no having to wrestle with tools like evil PowerPoint & Co.
SlideML only lacks a bit of tool support.. but now, as part of a publication not yet to be named, there is the WYSIWYG SlideML-Popoon-BXE Environment, gluing together BXE and Popoon (exaggeratory named "Cocoon for PHP) along with a syntax highlighting engine. An impressing PDF output pipeline remains still to be added, but Chregu and I just had that one day. We didn't even have to time to chat with Harry we coincidentally ran into.
I should say you'd better ignore the content of the demo presentation, by the way, due to the lack of quality it wasn't actually meant for publication. But if you want to try editing: Just browse the presentation and press the edit button.
I do like it the environment a lot, still I think I'll keep on writing my presentations the old-school way, directly hacking the XML. Much more comfortable than never-to-be-trusted WYSIWYG, to me at least. The entire package is open source (Apache-style), you can fetch it from the SVN repository. If you do, please fix the still numerous bugs :)
Oh, and by the way: the not-to-be-named book I mentioned promises to be pretty interesting, I think :)