I'm also using iPhoto 5.0.3 and have had no problems with this version of Keyword Assistant or the the previous version when used with 10.4.1. However, one thing that I've done before installing KA, was to always use their uninstaller to eliminate the previous version. This takes about 5 seconds.

I take some 10,000 photos a year, so adding keywords is a must for using smart folders. It's simple to use and has sure made categorizing photos a snap for me.

Thanks to the author for providing a great tool and for keeping it up to date.