Nothing draws the Google traffic on an election day like the words "exit poll," and the enterprising folks at the Chicago Current (a political newspaper and website) are using their own reporters and journalism students from Northwestern University to conduct an exit poll in Cook County (i.e. not statewide) and appears to be asking about the Democratic contests only (via Christine Matthews).
The Current's Geoff Dougherty has a write-up of what they are doing that includes some worthy disclaimers. Short version: exit polls have random error like other surveys (actually, more given the need for a clustered sample) and is "not the final score" when based on early returns, even if flawless. They are posting initial impressions here.
I cannot say anything about the methodology for the Current poll because, frankly, I don't know a thing about it. For those who have never read it before, you might want to consult my classic primer on exit polls, though remember that my advice was based on the methods employed by the network exit polls done by the folks that invented them and have spent decades honing their techniques.
Without knowing more about the Current poll, I'd urge extreme caution in interpreting the results, especially if your goal is to "call" the result. Remember, exit polls are most useful after the votes are counted -- when results can be weighted to match actual turnout -- in helping to understand who voted and why.
If I learn more today, I'll post it here.