LOL I think it's way funny that people buy cosmetics that celebrities say they like. Christina Aguleria most likely has a contract with MAC or Estee Lauder...whenever they're trying to get rid of a product, they just call her up and ask her to say she likes it, and BOOM! Two days later, they're sold out cross country and have room for the next product launch. And of course she gets free MAC makeup for life for these little shinnagens.
I think you should wear what you feel comfortable in, not just what Xtina (hah!) or anyone else is wearing. Be your own person!