One issue we’ve seen already is with Keynote 09 crashing on launch. Several users have reported that they had really old themes from the Keynote 1 days still installed on their system. You can also find an Apple DIscussions thread on the subject here:
You can probably find those old these here:
Hard Drive/Library/Application Support/iWork/Keynote/
The culprits seem to be Leather book and Sandstone
One user mentioned that you could still double click the theme file to open it in Keynote, and then save it as a custom theme, which fixes the issue.