While the Tribune ran a story at the beginning of the month looking at the economic impact of the Olympics, we decided to dig back even further into the past for an article a buddy of ours wrote a year before the Trib's version, even though it didn't appear on the Web until May 2006. It speaks in greater detail about how Atlanta buried some building costs in order to say they turned a profit.
Although Mayor Daley has claimed that Illinois taxpayers won't have much to worry about, recent history suggests otherwise. British taxpayers were recently informed that the bill for the 2012 Games jumped from an original estimate of $6 billion to $18 billion. When you combine that with the fact that Chicago has a history of screwing taxpayers royally, see Soldier Field ($660 million dollar reconstruction costs - 2/3 of which were paid for by taxpayers) and Millenium Park (which went more than $300 million over budget), it doesn't look good for Chicago if they get the Games.
One also has to remember that Soldier Field (seating about 62,000) is not capable of holding an Olympic capacity crowd. So a completely new stadium would have to be built or Memorial Stadium at UIUC would need to be upgraded even further than currently planned (which might not be such a bad thing).