I've noticed that, while viewing the map, the "Avoid Areas" function has a - quirk? idiosyncrasy? unexpected result - when you draw in a square area (Say, a large area from west Montana to east Minnesota, spanning both of the Dakotas north to south) and then pan the map east and west the drawn square appears to rotate sightly in place so as to remain perpendicular to the screen, and not the map (I suspect this has to do with how S&T interprets the projection of the map).
If you are expecting to avoid the areas covered by the square, you ought to place the area you want to avoid very close to the center of your screen, otherwise you may not be demarking the areas you appear to be.
[And that, believe it or not, is why this was posted in this particular thread. It took me a while to figure that out, and before I clued in, it appeared that the route S&T was sending me on went through areas I had wanted to avoid.]
Also marginally related to routing errors: Another quirk (Which has been carried through since at least S&T'05 in my experience) is that the expectation of rate of travel seems to be set much higher in the US than in Canada - resulting in S&T trying to route your trip through the states at every possible opportunity, at least when your preference is for "quickest route", anyway.
And while I've noticed that the estimates in Canada for travel time are spectacularly accurate (within 15 minutes for a 3-day trip, for example - Woo!), travelling through the US while trying to match the listed times for the various driving instructions would have been reckless in the extreme. Perhaps it could be done with the aid of a police motorcade, or in a low-flying plane...
Slightly further off topic, now, but...: A feature which would be nice to incorporate would be a warning for customs offices, which could behave just as ferry crossings do: Let you know they're there, and allow time for the stop. (Can you clear customs in less than half an hour these days? Anywhere? In either direction?)