Here's another small new feature, before moving back to some more weighty stuff.
Anywhere in Burp where you can view web requests and responses, you have a number of tabs showing different views and analysis of the message (plain text, hex, headers, etc). These tabs now appear and disappear based on the content of the message being displayed, and whether it supports the relevant view. There are also some new tabs for analysing messages, including colourised display of HTML and XML content. This view makes it much easier to visually scan a piece of HTML to see what it contains:
If you are editing an HTML response within the Proxy, you can also use the auto-colourising feature to sense-check that you have preserved the syntactic validity of the content, before sending it on to the browser.