Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
Although I do most of my professional writing in Bluefish, I usually use OpenOffice.org at least once a day. Consequently, I keep a close eye on the OpenOffice.org Extensions page.
These days, many extensions are language-specific or clipart collections that most people will never use. Others are filters for exchanging files with specific formats, such as Google Doc. Annoyingly, some recent extensions are thinly disguised advertisements for a company's service or issued under proprietary licences, although OpenOffice.org seems less plagued by these problems than Firefox.
Still, useful workaday extensions keep being posted. Here are three of the ones I've been test-driving recently: History Master, VisibleBookmarks, and Writer's Tools. All of them are installed in the usual way, by downloading them to your system, adding them through Tools -> Extension Manager, then restarting OpenOffice.org, although Writer's Tools does require some additional setup.