Go to the Nitty Gritty for cheap alcohol. There's really no other reason to go.
The Nitty Gritty is an okay place if you're looking for a bar that has good drink specials. Other than that, the Nitty Gritty doesn't smell good inside -- the front entry area smells like a frat house (old beer/dirty carpet stench), doesn't have very good food and doesn't have very good service.
I went here for a friend's birthday party. I ordered a drink and some cheese curds. Our server was either confused or frazzled because, although the restaurant wasn't very busy at the time, she kept forgetting things and needed several reminders from us. My cheese curds weren't very good and were likely frozen. I know fresh, fried cheese curds -- and these definitely didn't fit the bill.
You can't go wrong with a $2 cocktail, though. The birthday beer and balloons are a cute concept as well.
PS: Anybody older than 25 is going to feel really old at the Nitty Gritty. The vast majority of patrons are college students.