If my only option was to wait (i.e. no early turn outs) I would wait the full 3 minutes. I tend not to make allowances for smaller airliners, as it only takes one wrong id and you can be in a world of hurt. Wake turbulance is not something you take lightly, especially if you are not too familiar with it, or the airports operations.
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.
ATC: "Cessna 7JL, do you see the Southwest 737 on 4 right?"
Me: "Yes sir."
ATC: "OK, he is making a left turnout off the right side, you are going right off the left side. Turn right heading 130, climb and maintain 3000, caution wake turbulence from the seven-three, you are cleared for takeoff runway 4 left."
Me: "Right 130, up to 3000, cleared to go 4 left"tran 353, cleared to land runway 4 right." (Don't even let me finish!!)
I was holding in position at LGB in a 152 and a 737 departed a runway crossing my own. I was cleared for immeadiate takeoff after the 737 lifted off... this was about midway down my own runway and definately DIRECTLY in my flight path...
I really don't know what the controlers are thinking sometimes... You can really tell who flies and who doesn't with things like this. Needless to say I taxiied off the runway and waited the full 2 minutes.
Also wake turbulence can be a HUGE problem in the air. I once heard of a Bonnanza in the local practice area, located about 3000' under some of the airliners departure paths. It was a calm evening, and one second they were in level flight, the next the were 80 degrees nose down; good thing they had the reinforced V tail instead of the older kind... The scary thing is that I wouldn't have thought twice about an airliner passing that high overhead. It always pays to keep an eye out and avoid that stuff like the plague.
If you could see wake turbulence like you can tornados, pilots would say FAR, FAR away. Problem is that it's invisible though... the aircurrents can be 9000-15000fpm, which equals 95-130kts. If you hit a gust that big it could easily rip the wings off, much less throw you in any direction instantly.