And I am a Mac Genius!
It turns out that iTunes did not break all of my playlists. I broke iTunes!
Each time I turn my computer on, it automatically logs on to my home directory (my full name, one word) which contains all of my files and system preferences. Last week, I attempted to change the name of my home directory (under Macintosh HD --> Users) to remove my maiden name. Rather than removing the old name and replacing it with the new one, I inadvertently created a whole new directory ancillary to my original one. However, all of my system preferences and other user information migrated to this new user name.
I turned my computer on today for the first time since discovering my
iTunes mishap. My trusty computer logged on to my old user name, which no longer had any of my program or system preferences, so of course it couldn't recall my playlists, or my desktop picture, or even my Firefox bookmarks! This set off a little alarm in my head, so I decided to move all of my user information from the new home directory to the old directory (maiden name, grrr). I restarted my computer, and now all is back to normal. My system preferences have returned, as well as my old iTunes playlists!
I feel so sheepish. I wouldn't ordinarily go to the trouble of detailing this information on LiveJournal, but I sort of owe iTunes an apology. Its software did not erase any of my information; I did. Sorry, iTunes! You win!