There are... 6 guys working at my store. And 7 chicks. I think. We just hired a bunch of attractive people. I think it's because it makes people feel nice when pretty people are friendly to them. It's not that special if an ugly person is friendly.
It used to be more female-dominated but guys are good to work with. They're strong enough to open the juicer and scoop the yogurt when it's frozen. Also they can lift full bins.
I don't think product knowledge is essential, since you'll be asked to do some online quizzes and stuff later on. Know that there's nothing artificial and it's all low fat etc. Know a little bit about the company, say you drink Boost often, say you like the vibe and you want to be a part of it blah blah blah. Act like working at Boost would make you the happiest person in the world, and you just LIVE to make customers happy.
I read some interview / staff selection things today. They're looking for naturally smiley, attentive, happy people.