Many people continue to use iWork 09 apps, because they contain features missing in the newer versions. However, having the older apps on your system mean a constant nagging from Apple to update to the newer versions. If you do download the newer versions, then it is impossible to make the older apps the default for your documents. The old Get Info » Change All trick doesn't work.
Here's what to do to remedy that.
First, make a backup. Then install the latest iWork apps. Your older versions get moved to a subfolder called iWork 09. That's why you have the backup.
Next, move the NEW apps to an external disk or other partition. You can then restore the 09 apps to the /Applications folder. Or leave them in the subfolder if you prefer.
Having the apps on different volume from the system disk lowers their priority, so the 09 apps in your /Applications folder remain the defaults for your documents. What is more, any further updates will update the newer versions on your external drive, leaving your 09 apps untouched.
[crarko adds: I rather wish I had done something like this before updating. Maybe rolling back tp the 09 suite from Time Machine and then following this procedure will work.]
Mac OS X Hints