Most, if not all, of those mystery meat navigation menus work (I disable them all tho... I hate it when menues are obscured).
But sites like
http://www.deviantart.com/ , which basically rewrite the entire page a few times after load, don't.
ALL properly written sites using HTML2, HTML3, HTML4.01, XHTML, CSS1, CSS2, and/or Javacript (ECMAScript 1.3) work -- but only a few of the sites heavily relying on DOM.
Rather than going the IE way, and patching code untill it collapses on itself from the bloat, Opera is rewriting the entire browser from scratch now, so I'll wait for v7. Fortunately the web at large is only now starting to adopt HTML4.01, so there is time, except for those few experimental sites.
Besides, a properly written site always allows for navigation fallbacks.