Is the built in Nav software retarded or something?

OK can someone tell me if I'm just doing something wrong with the Nav software or is this thing simply retarded or poorly programmed. I live in the Minneapolis Twin Cities area and do a ton of driving each day all around the metro area. With the "departure" of the 35W bridge I've dropped a nice big square over the bridge in the Areas to Avoid section in memory. You would think that it would avoid this area but I would say that it does this in about 60% of the time, at best. As much as I would love to take a nice cool dip in the Mississippi I don't think I'm going to follow Mr GPS's suggested route.
This Thursday I'm driving to Chicago via I-90. I know there is going to be major construction going on near my destination so I drop not 1, not 2, but 3 points along areas to avoid that SHOULD force the software to hop off the interstate and use a local road...but does it...nope. It barrels through each point as if its not even there. :angry:
Are there any "tricks" to getting the software to actually follow your instructions. Because at this point the only thing I'm going to do is put a waypoint at the turnoff on the highway and hope that the thing is smart enough to stay on the side road the rest of the way. I don't really know the area there, and while I could start to pay attention when I get into the area and simply turn off when I get to the ramp after the amount I dropped on this feature it should work better then this.