Once I'd reached the point where I could squirrel away more than 30 digits a minute in memory palaces, I still only sporadically used the techniques to memorize the phone numbers of people I actually wanted to call. I found it was just too simple to punch them into my cell phone.
Moonwalking with Einstein: The Art and Science of Remembering Everything (ed. Penguin UK, 2011) - ISBN: 9780141952277