To really understand what the GPL licensing is all about, I thought reading the story of Dan Bricklin’s historical information about VisiCalc known to be the first SpreadSheet, should be helpful. His story about patents is quite a remarkable one. I found it really interesting. But wait! Here is the last paragraph of the GNU-GPL Preamble.
Finally, every program is threatened constantly by software patents. States should not allow patents to restrict development and use of software on general-purpose computers, but in those that do, we wish to avoid the special danger that patents applied to a free program could make it effectively proprietary. To prevent this, the GPL assures that patents cannot be used to render the program non-free.
Now that my favorite part of the Preamble is there as a reminder, here is the website I was referring to: http://www.bricklin.com/default.htm