For me, I never really wear a lot of mascara, because it really depends on your eyelashes. I wasn't really born with a lot of nice long lashes so when I went to get make-up consulting, she told me that I didn't really need to wear any. Sometimes the natural look is the best.
If you really want to know what kind of stuff goes into mascara that makes you think it's "making them longer", then I think you should book an appointment at your local mall's makeup store. I know places like Clinique will do it for free, if you ask for make-up consulting. I actually prefer a lot of Clinique's products because they are designed for sensitive skin. They just seem more natural.
