Not sure where gbadman is, but a similiar situation I often see at the circle interchange in Chicago waiting in line (as you should do in that case) can easily cost you several minutes.
I'm in Montreal. We have a serious traffic problem during morning and evening rush hours. In fact, TomTom has put our city at #4 in North America for worst traffic and it seems #1 for both morning and evening traffic peaks [1].
Two places that I can think of this being brutal are taking Decarie Blvd exit from Decarie North and taking the 20W exit off of the 13S. I'm sure that are some other pretty good examples out there.
I'm asking in all seriousness, I have no idea what sort of traffic you are driving in.