So I don't know what sort of businesses will use this site- but Groupon is basically a marketing tool for businesses and a way to offer great deals to customers. They have been in many other cities, but today is the first time they have an offer in Detroit. There is a Deal of the Day every day for a different local business - and once a critical mass of customers show interest, everyone is eligible to purchase this deal.
For example - today, for $35 you can get $100 worth of hair services at Flip Salon in Ferndale. I am assuming/hoping that every day will be a new service/product offering from a local business.
I like this idea- it is helping local businesses reach a broader customer base - and it's helping poor folks like me try something out that might normally be a bit out of my budget.

Check it out if you are interested - http://tinyurl.com/yfyyblb