My mother got it, and she never really has that big of an earnings bonus, but has had it for a few years now. Sometimes it's just completely random, and other times people say they base it on data of what cars you currently own and/or information you've requested about new models.
Problem with us is, once it was right AFTER she bought one truck, then later again, and now she has the $1000 bonus on top again until about mid March, but really no idea if it'll even be considered for use--I kept it just in case.
Also, that said, there was a glut of people who also got separate bonus mailings about a month ago, but I don't think we got one of those.