I'm going to be going over the 3.1 features in the next few blogs. Here are a few that are just nice -- not groundbreaking but very nice, convenient changes that making interacting and collaborating easier. The third just makes slight annoyances go away a little more easily.
Replying to Notes
In 3.0 the notes are new and improved by being in boxes off to the side. Now you can click and hold down on the black arrow, and reply to them, too. The reply shows up immediately below the original in a contrasting color. (You need to be a different user, under Tools > Options > OpenOffice.org > User Data for this option to be available.)
Easier Accept/Reject of Changes
It's also easier now in Writer to accept or reject a change when you're tracking changes. Just right-click (as I like to say, when in doubt, right-click).
You could always remove a hyperlink by selecting the text and choosing Format > Default Formatting, or right-clicking on the selected link and choosing Default Formatting. However, this makes it more obvious. Right-click without selecting and you get Remove Hyperlink as an option, as well as Copy Hyperlink.