I am aware of what the law is, I was wondering what actually happened.  Did the people who run the building just ask the carrier to leave, did they arrest them, call the police, or run screaming with their hair on fire?

No one?  It does not have to be you personally.  I am not the PoPo, if that is what you are worried about.  My buddy and I were just wondering what some of these folks would actually do, since many of them just put up the signs and never read the law nor do they know what to do.

We try to track that sort of thing at IllinoisCarry.  I've asked and the word I received is there was one case where someone someone was charged but, it was dropped.  
That is amazing when you figure how many folks have a CCL and how many "prohibited places".

My thanks to Swanhunter for the info.  From what I have gathered on this subject such incidents are rare or at least do not make the news.
My wife and  I went to a court house today and I did a pocket dump before entering.  They did not have metal detectors at the door, we went to the county clerks office and did not see any security.  Other counties have metal detectors at the door.  I have not forgotten yet that I was carrying, but it would be easy to get into a situation where you did forget.

Surprisingly few no gun signs here in Dekalb. Only one I've run into at a private business was a liquor store. Inappropriately named "American Liquors" 
I haven't heard of anyone getting busted or being asked to leave.
Only time I have to take my carry off is for the post office.