Business casual is kind of hard to define. My understanding is the same as yours, Betarulz: khakis/slacks, polo, maybe a sweater. No need for a jacket or tie, and no jeans or t-shirts.
It's even harder to define for women. In the business-casual work environments I've been in, I normally wear a nice blouse and slacks, and nobody's complained. (I actually dressed the same way when I worked for a dot.com. People were perpetually asking me if I had a job interview.
)
Has anyone else heard of "black tie optional" ? Nobody's mentioned it yet. Black tie optional (at least around here) is "we'd prefer that you wear a tux, but you could get away with a suit".