I was 90 percent sure that my face wouldn't in fact look all horrible and scrunchy forever and ever. Anyway, I eventually outgrew my penchant for making faces at people who annoy me - thank goodness, or I'd never be able to keep a job. You probably are not aware, but both ubiquitious chains are at the forefront of scaring the bejabbers out of privacy freaks like me. Right now, the technology is used only in check-cashing machines. Because right now that's the limit of what the machines do.
Customers have to ask to be part of the program.
But as with all technologies, narrow applications become widely-used applications, and that's where the concern is. They could very easily build a customer database that could be sold, without your knowledge or consent, to anyone who asks. You think the telemarketer calls you get now are obnoxious. Not at all. And mere marketing might be the least of our worries.