Dear Splate
we all had this problem with Keynote and large files and Apple is not capable of solving it (since the last 2 years???) just unbelivable!!
Here I get you the helpfull thread thanks' to Fuzzydog. This worked for me!
I have found only one solution and it only works for those of us who have a iwork disk to reinstall from. Those who downloaded from the app store are I think out of luck unless they managed to save the downloaded .dmg somehow.
I have downgraded iwork from 9.1 to 9.05 and have had no problems in keynote since then!!!
Here is how to do it.
1. Remove iwork 9.1 using the script supplied by Yvan Koenig. See this post in a pages discussion with the location of the file. https://discussions.apple.com/thread/3272551?answerId=15969759022#15969759022. If this link doesn't work go to the iwork discussions and search for his name and "remove". It will get you to a post of his with the link to the script. If you do a manual uninstall you have to do more than simply remove the iwork folder from applications. Try using easyfind to locate all iwork files. There are many spread throughout your system. Make sure that the following folder is uninstalled before you reinstall the earlier version as a reinstall of an earlier version will not overwrite them. ~/library/application Spport/iwork '09/Frameworks.
2. Reinstall iwork from your disk.
3. Update iwork to version 5.05. You can get this here. http://support.apple.com/downloads/#iwork.
4. When you restart iwork check the version number to make sure that it has been successful. If you reinstalled without a successful total removal it will still show version 5.1. The script mentioned in #1 above does not remove your personal templates stored in your user/library/application support/iworks folder.
5. The first time you open an iwork app it will ask you to upgrade to 9.1. Do not do this and check the box indicating not to be reminded again.
The fact that 5.05 works flawlessly under Lion proves that version 5.1 which has the offending autosave features for Lion is the cause of the problem. 5.05 works great in Lion. No issues. Manual saves like the old days. No spinning ball down time (except on command S saves which still take a long time but that is the same as it ever was for big files with lots of media).