On my way to a client's I've listened today to the latest hanselminutes show titled "Open Source Software Licensing with Jonathan Zuck of ACT Online"
this show is a must listen for every developer that uses 3rd party code downloaded from the net, and is liable for his creation.
it's a great introduction to software licensing and patents and clears some uncertainties when using common licensed libraries (like GPL , LGPL , BSD ect').