Extracting layers from Paint.NET

Paint.NET doesn't seem to be able to do this natively. Take a look at the utilities on this page:
http://www.comsquare.ch/index.php?option=com_content&task=view&id=36&Itemid=55

Specifically, pdn2png can save each layer into a separate file with the /split option, like so:

pdn2png /split yourfile.pdn

Alternatively, for something with a graphical interface, try this:
http://forums.getpaint.net/index.php?showtopic=9704

I did a quick test with a 2-layer PDN file, and both seem to work as advertised.