Yes I memorized my seed phrases. 

Of course I have them backed up as well.  All the typical ways.  But my PRIMARY way is my memory.

Anyway, this is how I did it. (I'll use a 12 word seed as an example, but I actually did it with a 24 word seed phrase).

FIRST, I wrote them down (of course).  Tried to repeat them back.  Failed of course.

Then I split them into three four-word groups.  Wrote each group on a notecard.  I concentrated on learning the first group of four. Once I could recite those four words back, I went on to the second group. And the third.

Woke up the next morning, could only remember the first group.  Repeated the exercise.  Over and over.

Finally, when I had burned all three groups into my memory to my satisfaction, I made a new set of three cards.  This time with only the first letter of each word.  So, each card had only four letters.  This enabled me to further burn the words, with repitition, into my memory.

I tried repeating (in my head) the full seed every morning upon waking.  If I failed, I consulted the cards with only letters.  If I still failed, I went to the cards with the full words. 

Eventually I really no longer needed the card with the words.  So I burned those, and created a single card with four letters, the first letter of the first word of each group. 

I went on, repeating (in my head) the full seed every morning upon waking.  If I failed, I consulted the single card with only four letters.  If I still failed, I went to the three cards with the four letters each. 

Rinse and repeat.

Eventually I no longer needed the three cards with four letters each.  I burned those.  At that point I only needed the single card with four letters, the first letter of the first word of each group. 

.............

I still repeat my seed phrases in my head every morning when i wake up, and havent had to look at that single card for a loooong time.  It's also been burned.

Anyway, that's how I did it.