When flying out of CMI, I'll analyze the current winds and make a determination of when to takeoff. I've departed following RJs, Saabs, and Jetstreams often with about 1 minute separation. If the winds are strong, or right down the pipe, it's much better than a light quartering headwind or tailwind in regards to wake turbulence.
I should also add that I fly out of MDW often, and the controllers don't know what wake turbulence is I think! I get shot off 4L with a 737 or 757 departing 4R on a left turn out often. Same thing for 31C. You just gotta watch their departure path, and make all attempts to avoid flying through any wake.
MDW really is an eye-opener.