But what will happen to my keywords from iPhoto 08 / 09 ?
Your keywords will be migrated when you open your iPhoto '09 library in iPhoto '11. The events, albums, smart albums, keywords, titles will move over. If you have photo books, they may change slightly, because the themes have changed.
But as a precaution, do not upgrade your iPhoto Libraries to the newer versions without keeping backup copies of the libraries.