Thank You! Thank You! Thank You!
We've been using WYSIWYG editing in tons of programs for years. It slayed me the first time that I went to edit/write something in Wikipedia when I encountered the regular editor. While I've gotten used to it over time, the beta option is a giant leap forward. Nearly does away for the need of the preview button, though I like the idea that you kept the Edit Source option.
Hope this gets implemented soon!