If you want to save your Wiki content and settings you just have to allow the browser to re-save the local HTML file – using that it will just overwrite itself and remember its changes when you re-open the file in the future.
TiddlyWiki is intended to be used as a single user Wiki mostly, ranging from a powerful notebook or journal to a tool to document all your work. Since it creates backup copies of its previous state upon saving, you don’t have to fear losing all your work at once in the future.
I think it is really great fun to use and marks a new step in browser based software. After playing around for a while I quickly understood how to use it and what benefits one might gain from such a tool.
Try it out for yourself and have fun!