It is quite alluring actually, because she's the type of personality that doesn't take herself overly serious and is willing to relax and be herself, rather than being tense and uptight around others. When you're with a girl with a good sense of humor and knows how to laugh at life and understands how important that is, then you are more at ease with the relationship as well and it will go smoother getting to know each other; without that it takes longer and more patience and that's not necessarily a bad thing in some incidences, but in general, it just makes a girl more appealing if she's got a good, health, sense of humor about her.
Equally as important as it is for women. I never hear anyone of either gender say they don't want someone that has a sense of humor. I think it goes without saying. Like dating profiles etc, listing you want someone with a sense of humor doesn't need to be said, of course you do, we all do.