The best thing to do is call your local favorite stores. Since you posted this on Apple, Industry and Internet Discussion, I'm guessing you mean Apple stores, but this applies to all stores. Go ahead and call. Stores LOVE black Friday for sales, and often have door buster sales to get people excited, and they'd love to share their BF specials with you over the phone.
Its the day being begin the rabid christmas shopping. Historically stores tended to have crazy sales, especially in the wee hours. With the current economic situation, I wonder how things will go this year.
I'm not one to venture near the malls on friday because traffic will be so bad. What's on sale? Generally most things, just look online for black friday flyers. There's plenty of sites posting them and you'll see what's on sale.
Personally saving a few bucks isn't worth the hassle.
The Black Friday discounts are normally $101, EDU discounts normally result in $100. Despite the "modest" and limited discounts this is important because it is the only time that an average person without any special status (government/education/etc) can walk into an Apple Retail Location and receive a discount.
We do have a guide chronicling the history of Apple's Black Friday.