Well, it really depends on how bad the typo's are. It also depends on how selective the school is. If all things are equal, I'd usually go for the person who had reviewed their application to ensure that there was no typos, as I'd think that they'd be the ones who'd rather be at my school!
So, yeah, it might hurt you, but there are many different factors influencing your app. And if it's already in the mail, then just go have a beer, as there's nothing more you can do!