The basic idea is that people still don't want to do a lot of fancy formatting that you will find with the common HTML WYSIWYG controls. Wikis don't compete well with MS Word, nor is MS Word very usable because people waste too much time formatting. Similarly, people like WikiSyntax. So, give them buttons and some visual feedback, but keep all the power of WikiSyntax.
At this point, still at 0.10 and not 100% working, but definitely heading in the right direction. It only works in FireFox? currently.
It may appear at WikiWikiWeb in the near future. It's available for [download] off of JSAN.