WordPress 3.4 is coming along rather slowly. It should have been ready by now, but progress has been slow and we're only now at the second release candidate stage.
But it shouldn't be long now, the final build should be coming soon. WordPress aims to have it ready by early next week and, unless some really big bugs show up, it will be so.
There may still be some bugs to uncover, though it's probably safe to install WordPress 3.4 RC2 even on a production blog. There's still a risk though, so better wait until next week.
While there may not be any more bugs in WordPress 3.4, there may still be incompatibilities with themes, plugins and so on. This is probably your last chance to test whether your themes and plugins work with the new version of the blogging software.
WordPress 3.4 RC2
is available for download here