Great choice and location for race day!
I stayed at the Conrad for one night before the Rock-n-Roll Half Marathon in July 22, 2012. The location is great, close to shops and restaurants. The next morning, we had only a 15 min walk to Grant Park, where the race started. The staff was great, on race day I forgot to get safety pins for my race bib (needed to pin bib to my shirt). I went to the front desk to see if they had safety pins, and the front desk manager was my hero. He had a small box of pins for me to get the four pins I needed. This saved me a ton of time in trying to find an open store at 6am in the morning or worrying about how to attach my race bib. We visited the Terrace Rooftop lounge the night before. It was a nice relaxing place to have a nightcap and chat with friends we met that evening. 
Parking is expensive ($52 valet-overnight), but you have to remember you are downtown Chicago in a prime location. In staying there you need to calculate the cost of parking if you have a car. This way the total cost of the stay can be figured out a head of time, and you won't be shocked at the end of your stay. For a one night stay the cost was acceptable for us.