50% off discounts attract the wrong customers, who I call uber-deal hunters. These deal-maximizers come simply for the big discount with little intention of becoming full price patrons.
This is exactly what I thought when Groupon first came out. I remember doing 2-for-1 coupons at my families restaurant in California when I was a kid and we were very busy, but the customers never came back. I quickly came to realize that the customers who look for those deals are always looking for the next big deal, not the next best product. I like what Rafi has to say, smaller discounts for trial has a better opportunity for repeat guests.