Yep, Its nearly update time to update your WordPress site again, but i must say that this time around there has been a fair time between drinks, with just 2 minor security updates in between major version updates ( as of writing this article ), it has been pretty smooth sailing for the Tiger Strike Media team.
With many people still coming to grips with the new features from WordPress 3.3 the core team wanted to put a firm focus behind the scenes with performance improvements in many areas of the site, and a massive improvement in the database querying which will massively help very large databases.
With nearly 480 tickets slated for WordPress 3.4, there are a lot of changes taking place to the WordPress software, but ultimately the changes you should see in your WordPress site will be very minor, things like HTML will now be supported in image captions, Improvements to the custom header functionality and many other small UI changes.
Under the surface or WordPress there have been improvements to the help screen api, i18n, database queries and much more. You can see the codex page here and noticeably, not a lot happening in the UI department, but a lot of work in the stuff that developers will understand.
Basically, this version of WordPress will be a smooth update for everyone who has a normal installation, and standards compliant themes and plugins on their site.