The idea behind GNU GPL was not first clear to me. I first understood that everything under this license is free of charge, but actually no, there also can be free programs that still ask for some fee but in return give user/developer the right to modify the program unless they keep it to themselves. Probably I use programs under this license every day, but as most of internet/computer users, including me, do not read user agreements, I have not noticed it. As I am not a developer I also have not modified it by myself.. but I have used modified programs, most of all Mozilla Firefox, which has different capabilities done by different developers, although the "original" version is also quite good :P
The strength behind GPL is mostly that every person can be sure that she/he can share his/her programs and at the same time it is protected as well. The biggest fear with allowing others to use you prgram for free would actually be that someone of them might take the program and decide to register it for their name. It would mean that the original developer would not get credit (I am not talking about money here) for it.
As programs are free to be developed it gives the opportunity for them to evolve quickly. " heads are always better then one and if first developer does nto seem to have more new ideas, it does not mean that with brains trom or just different point of view it could not be done. This is actually definitely a weakness for big companies sofwares that are really hard to manage and changed.
