Sigh... Nvu (1.0 final release, not PR!) is a good start: not because it's a good WYSIWYG html editor, but because it's the ONLY free WYSIWYG html editor available for Mac OS X. Sadly. The work that has been put into this software is very highly respected, and things can only get better from here on.
I'm sure Nvu is great if you just want to hack up a couple of simple pages without needing to know about HTML. However, if you do professional web design, you can safely forget about Nvu at this stage. There are just too many inconsistencies and bugs if you really need to rely on the details and focus on high-quality, elegant code.
You can only switch between HTML 4 and XHTML 1 and between transitional and strict DTDs, and that is not honored correctly (if set to XHTML, an HTML 4 header is inserted anyway). It does the most vile thing a web editor can possibly do: it automatically reformats and changes your existing code, even if you tell it in the preferences not to. If you use inline CSS formatting, it inserts a huge bunch of completely unnecessary CSS formatting statements. This is about as bad as it can get; a regression to the bad, dark, old world of the web-editing stone age à la Claris HomePage (1997). Not good!
To sum it up, if you're still stuck in the HTML 4 era (1997-2000), and don't care about what's happening in the background (i.e. code), Nvu will be quite a useful piece of software. If you're going to do state of the art web development (using XHTML 1 and CSS), Nvu will not work for, but against you. It's more fun developing with a standard text editor (as before) than wasting time editing out the bad stuff Nvu automagically puts into your code.
The interface looks very promising but needs a lot of polish. There are some nasty bugs that absolutely shouldn't be in a 1.0 final release, like if you close the last document window, the menu functions for creating or opening a new document no longer work; the only way to get out of this is to quit and re-launch Nvu and then open a file from within the document window that's created on startup.
So -- looking forward to a hopefully bright future viz. open source WYSIWYG web editing on Mac OS X, and may the force be with all developers working on such a project.