The offers only show up when the Kobo is asleep, below the title of whatever you're reading. It's pretty much all ads for sunglasses and how-to-use-your-Kobo tips. Unfortunately, I haven't seen any updates to the ads. I don't mind them much, but they do get old. And it'd be kinda nice to have the book's cover show instead. But hey, I was in a hurry to replace my old reader, and that's what was in stock in the store that day.
More info in
this previous thread.