Where are you going? If he is taking you out for a hotdog and a ballgame, sure jeans would be fine. If you showed up in a dress and heels, I would suggest doing something a little nicer unless that is what you were comfortable wearing (and I would consider myself VERY lucky)
If I say, hey, I am going to fly in and I would like to take you out for a nice dinner (that means a real restaurant not a chain such as Chilli's or J. Alexander) and you showed up in jeans... it would not make points with me.
Forgive the uncultured swine who don't know what different types of dresses there are besides formal gowns. A sundress is your best bet for a first date, it is cute, fashionable, casual, and feminine. A casual dress that accentuates your femininity is always the best. Jeans are just distasteful on women, in my personal opinion.
It's entirely based on the venue of the date. Now if a guy knows anything about women, he will clue the woman in so she won't A: over think what she should wear and go crazy, or B: over dress for the occasion.
just to make it so that theirs no generalization (as shown through the other three guys) I will go with dresses...not only because I wanted to break it up...but because...i myself like them...im not a huge "jeans on girls" guy...i mean yeah once in a while its fine...but it shouldnt be all the time