WordPress 3.4.2 released today. I did a quick upgrade on my WordPress installations.
It is a security update, so, do not wait.
Fix some issues with older browsers in the administration area.
Fix an issue where a theme may not preview correctly, or its screenshot may not be displayed.
Improve plugin compatibility with the visual editor.
Address pagination problems with some category permalink structures.
Avoid errors with both oEmbed providers and trackbacks.
Prevent improperly sized header images from being uploaded.
It is time to update.
Keep update is the way to security your website.