As an experiment, I trashed some files and emptied the trash. They still showed up in Spotlight, and could be opened. I did a restart and they still showed up in Spotlight. There was also a new "recovered files" folder in my trash bin, although it was empty. Does this mean Spotlight can be used as a file recovery utility?
I then secure-empty-trashed some different files, and they did not show up in Spotlight.
Also, Spotlight has a privacy function where you can tell it to skip certain volumes/folders, but you can't do that until after it's already indexed everything, which sorta defeats the point. Am I missing something?