If you're feeling gutsy, try this with your users. If you're not ready for that, try it with colleagues (see below for a few alternative prompts).
Prompt for patrons:
Librarian-anthropologist Donna Lanclos invited students at UNC Charlotte to do this for the campus library. Take a look at what they love, and what they could live without. (Hat tip to Deirdre Costello for sharing this with us!)
If you want to try this with co-workers before taking it out in the field, here's some alternative things to write a love or breakup letter to: