I don't have iWork, so I'll leave comments to someone else.
But I do use Open Office on the Mac
http://www.openoffice.org/
I've been working with the beta native Mac port (Aqua) and have had some fun with it. You can find it here:
http://porting.openoffice.org/mac/download/index.html
The straight OO distribution runs very poorly on Leopard though (in my experience).
For free, it handles all Office Documents except complicated spreadsheets and word documents involving a lot of tables. Plus it has a built in PDF printer. I wouldn't use it in a business setting, but for personal stuff it works great!