If you are visiting Chicago, stay downtown or close by (O'Hare is 25 minutes on the CTA Blue Line). You are visting the city, you don't want to spend all your time traveling to your destinations.
Magnificent Mile is pretty cool. If you want to tour the buildings and such, the Chicago Park DIstrict has iPod MP# walking tours free on their site. You can google it and they will come up. Nice way to spend an afternoon.
Then, go to the Hancock Building's 95th floor SIgnature Room (enter on the South Side of the Hancock). It's a $$$$$ restaurant, but there is also free lounge/bar that gives you better views than the Sears Tower, and you can have a nice beer to quench your thirst. Never any kids up there either, so that's always a plus.
I highly recommend finding a friend in Chicago who can be your unofficial tour guide. They can tell you what's happening, and help you plan your stay. A couple nice sites to visit prior to coming are Metromix | Your Restaurants, Nightlife & Events Guide
and also www.chicagreader.com
. They will give you all the haps.