Apple's installaing Keynote 2 into the iWork sub-folder of applications may seem like an unnecessary annoyance to some, but it does have one potentially useful consequence: because the preferences and application support files for Keynote 2 will not overwrite those for the original version of Keynote, it is possible to switch between versions of Keynote -- or even run them both at the same time! Arguably this is of limited utility, although it might be helpful for those with either a lot of time invested in the original user interface. It might also be useful should any existing documents not open correctly in Keynote 2 -- not that I have encountered any such presentation files yet.
Specifically, both versions of Keynote will use any themes saved at /Library/Application Support/Keynote/Themes/; preferences for version 2 are written to ~/Library/Preferences/com.apple.iWork.Keynote.plist, while the original version's preferences are in com.apple.Keynote.plist.
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http://hints.macworld.com/article.php?story=20050122222822694