I think there is a difference between people bitching in private, and it being something publicly searchable by people who just met you. One bad date and suddenly you have a reputation that follows you forever? (Assuming people used this app of course)
Oh, definitely, that's why I added the last paragraph.
That being said, I would find it a good indicator, if the person you were dating took notice of this drivel, they are probably the kind of person you don't want to be dating anyway.
I think the biggest issue is the complete anonymity which is inherently given online, even if it asked for identities, these can easily be faked.
What is to stop a jealous co-worker or an annoyed sister, or even a drunk friend from tarnishing your public image online by saying you treat them badly, or even worse, raped them, over an application like this?