I've been doing 2D details all week and the most annoying thing I've run into is that polylines will not trim using the Ctrl + Click method. Lines, circles, arcs, walls -- almost everything else will trim with Ctrl + Click, but not polylines.
Running a close second is the fact that you can't Unify a line or polyline into an existing polyline. AC turns the new segments into a polyline, but they won't be connected to the original polyline. You can unify all day without success. The only way to get all the segments unified into a single polyline is to explode all the polylines you are unifying, then unify the resulting line segments.
