I switched from MS Word to Apple's Pages (part of iWork) a few months ago, and have been very pleased with the decision. However, there is a very important feature that you really ought to use in case things ever go wrong with your hard drive. When you first save a Pages file, there's an checkbox at the bottom named Include preview in document.
What this does is save a PDF inside the .pages wrapper (Pages 'files' are actually folders, like applications). Why is this a good idea? Well, for one thing, some file recovery programs such as Data Rescue II will not recover the .pages files, but will recover PDFs.
I learned this the hard way after accidentally (and unknowingly) deleting a folder where I keep most of my personal documents -- which was also gone from my backup drive because I updated the backup before realizing the folder was missing. Data Rescue II did a remarkable job finding deleted files (it rescued 14GB worth of deleted files from a 160GB drive with 111GB currently in use) and it found many old Word .doc files. However, my only hope of recovering my more-recent Pages documents were the automatically-generated PDFs.
I guess a corollary lesson here is that if you want something really deleted be sure you use Secure Empty Trash from Finder -- some of these files recovered are from 6+ months ago!
Final Note: although I am describing my experience with Pages, I believe the same problem above would exist with Numbers and Keynote files. Both Numbers and Keynote also support the Include preview in document option. Don't forget that Data Rescue II might be updated in the future to support recovering iWork-specific files, so check the website for the latest information.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20071017204817322