If you are working on a polyline it is probably a good idea to CLOSE it. In 2012 if you first SELECT the polyline with a left click, you will see a great many grips. On each segment, between the vertices you will see an additional grip, which can be used for converting to an arc, or adding another vertex. If you hover briefly over any of the grips you will see a 3 item drop down menu which includes ADD VERTEX. You can very easily add as many vertices as you wish. I am not sure if this was in 2011 or not. It is a real improvement for grip operations and manipulation. In the attachment you will see a group of vertices which I added to one straight segment of this polyline.
I just checked, and this feature is also available in 2011. The 3 options on the drop down are STRETCH, ADD VERTEX and CONVERT TO ARC. These are really helpful options which can be used on every single grip on a polyline.