Wordpress is moving towards being the most useful CMS tool for publishers and 3.1 release is mostly aimed at solving publishers pain points.
Easier Internal Linking
You’re writing a post (or a page) in WordPress. You mention something you’ve written about before, and think to yourself, “I’m going to link to that last post!” What do you do? You might open a new tab and search for the older content in your dashboard’s list of posts, or you might go to your live blog and find it. Either way, you have to find that content and get the URL, so that when you click on the link button in the post editor, you’ll have it ready. Right? What’s that, 5-8 steps, depending on which way you do it? No more!
You can now enter any URL to create a link just like you used to, OR you can search your existing posts and pages right there in the link popup. A combination of pre-loading, autocomplete, and some ajaxy goodness make the new link creation tool a joy to use (and man, that popup is so much faster!).
When you’re in your dashboard and you click to the Posts section (or Pages, Media, any screen with one of those listing tables), do you ever wish you could click a column header to change the display, like to sort things by date, alphabetically, by author, or other criteria?
Ajax Search Results
Reviewing search results will be faster and no longer require screen refreshes in the dashboard, thanks to the addition of ajax to the search results screen.
Other features include better IE9 support and the revised blue color scheme (details here).