I always have the setting
Automatically write changes into XMP enabled. Unfortunately as I'm still often improving/experimenting with my workflow, I tend to delete/create catalogs every once in awhile. For this reason, I also have refrained from using more of the collection-based features e.g. keywords because I'm afraid I may lose some data when deleting a catalog.
What data is stored exclusively in a LR3 catalog? And if I delete a catalog, what data will I lose, if any?