AnalogSanity

That is called antialiasing. When zoomed out it gives the appearance of a smooth line / curve. If you don't want antialiasing enabled simply select the line tool from your tools menu and from your menu bar choose to disable antialiasing. The icon is a blue line with three circles on it.

Let me start by saying Paint.net 4.0 is awesome.... however the latest alpha release is crashing every 15 to 20 minutes for me. Is there some way I can send you the logs?

Awesome thanks!

I love paint.net!!! I am a web developer and have used this app it since 2006. One feature / option I would love to see in a future release would be the ability to set the outline of an object or line object as dashed instead of solid.