While unsubscribing from some Xerox e-mail, I came across this rather nice little questionnaire. (Click image to enlarge.) I thought it was short, had a good range of options for me to choose, and looked like it would probably help them understand their subscriber stats.
The truth is, I'm just not engaged with their category right now. I was shopping for color printers a year ago, and seriously considering their solid ink option. But ultimately went with a color laser.
Perhaps they could have added the option, "just bought competitor product" or something like that, but this questionnaire is still miles better than anything else I've seen on an unsub page.