I never needed the mnemonic. I didn't even need to memorize the planets - I just read about them (when I was six or seven) and knew them.
Tommyrot is me. From 4 until about 10 or so I was absolutely fascinated with both dinosaurs and astronomy.
Roy G. Biv is the way I learned the order of colors in the visible spectrum; never thought about it before it was presented in class in grade school.
But JenP is me in this case. Though I actually think I got it from a PBS program of some kind long before I was taught it in school. I remember taking art class in highschool and wondering why so many of my fellow students had trouble remembering what colors you had to mix to produce other colors.
And now discussing PBS and colors has earwormed me with the theme from Reading Rainbow.
"Always remember that there is 'a rat' in 'separate'!" I've never had problems spelling that word since.
I saw a flash card type thing where the word separate looked like it was broken apart with a giant "A" in the middle, which always springs into my head whenever I write the word.
And a friend's SIG was "People Can't Memorize Computer Industry Acronyms" for a while.
One of my favorites along those lines has always been System Cannot See It.