very important. but somehow i think eyebrows are usually neglected, at least comparing to eyes. they just help to shape your face, bring out your eyes, they are the best supporting actresses.
personally i have fairly thin eyebrows, which i am bit ashamed of.
i don't put makeup on them, but can't go out without draw them just a little bit, though lots of people said mine have beautiful shape, which is a bit archy.
still, i can't leave home with naked ( albeit in good shape) eyebrows.
so yes, they are very important.