I'm in the process of moving from an ancient Joomla 1.5 site to WordPress and this made the difficult chore of transferring the content as easy as it could be. The plugin's function for cleaning up internal links after import is a godsend, and since I'm on a shared server, I really appreciate that the plugin resumes where it left off if the import is interrupted by a server timeout. I would have been cooked without that feature!
The only minor criticism I could make is that it would be helpful to note that your WordPress database's post table will probably be in serious need of optimization after the import is completed. That's not difficult to accomplish via phpMyAdmin or one of the WP optimization tools, but it's something to remember and I'd love to see a future version of this plugin provide an option to perform the optimization automatically after the import.
Even so, this is an invaluable tool if you want to move from Joomla to WP.