[tlug] GPL and Open Source Licences

[simon colston <simon@example.com>]

If I link to some GPLed code I understand that I have to licence my code 
under the GPL too.  If I then distribute my program I understand that I 
  also have to distribute the source code as well.

Under the GPL, do I also have to distribute the source publicly too? 
That is, do I have to make the code available to _anyone_ who asks for 
it or can I restrict distribution of the source only to the people I 
distribute the program to?

Is this the same for all "Open Source" licences?  For example, the 
Apache Licence, Mozilla Licence or BSD licence.

I know that probably none of you are lawyers so I will not take anyone's 
answers as any sort of legal advice but I would be grateful to hear your 
opinions on this subject.

-- 
simon colston