For those of you who might be interested in knowing more about the properties of the woods that you make plugs from, there is a free publication available from the Forest Products Laboratory called the "Wood Handbook".
It is arranged as a series of downloadable PDF files, one for each chapter. There are many tables of wood properties and the chapters in general are quite readable, being meant for public consumption.
Here's the link:
http://www.fpl.fs.fed.us/documnts/fp.../fplgtr113.htm