Saying "I'm an aerospace engineer," or "I enjoy reading Don DeLillo" sounds much more intimidating than "I'm, like, an engineer," or "I enjoy reading, like, Don DeLillo." Maybe women of my generation have been taught, through positive social reinforcement, that we're supposed to pepper our speech with meaningless modifiers that make us sounds a little less sure of ourselves, a little less credible. No one likes a show off or a know-it-all.
Hm. Maybe. But--being a native of the San Fernando Valley, which is ground-zero for the emergence of "like"--I've always felt that the word truly is a meaningless modifier, and isn't meant to convey any sense of vagueness or uncertainty, but rather serves to give one's overall speech a certain kind of cadence and tone. In other words, it's just one of those linguistic traits that emerged arbitrarily, and doesn't carry with it any semantic or other significance--just like a dropped t or something.
Of course, it can be the case that speaking this way makes you seem less serious or intelligent, but that can be explained purely by social convention--usually any dialect that strays too far from what is by convention considered the elite dialect will cause listeners to take the speaker less seriously. That could be a heavy Valley-girl dialect, but it could also be a syrupy Southern drawl, or Ebonics. So it's not that the word "like" causes one to be less serious, per se, it's just that that word is the hallmark of a particular non-elite dialect, and having that dialect is what affects elite listener's interpretations.
But who knows?
