As reported by MacStories, it looks like Apple have quietly stopped offering free trials of their software, including iWork. The page which used to provide the download now simply says
The trial version of iWork is no longer supported. But you can easily purchase Keynote, Pages, and Numbers from the Mac App Store to start creating beautiful presentations, documents, and spreadsheets today.
Which is great, except that that download was also the only digital distribution for iWork licenses – like mine – purchased before the App Store existed. So, if I hadn’t had the presence of mind to hang on to the installer, I’d now be stuck with a useless iWork ‘09 license and Apple’s official response is to suggest I re-buy the exact same software from the App Store.