Adam Farkas wrote:
You would have to release the source code, _if_ you built this commercial product and intended to sell (redistribute) it to a third party.
[...]
If, however, you are working on custom extensions for a client (as we at ArsDigita do for a living), and don't intend to have that client re-sell or redistribute the code that you write, then you should be OK.
So you circumvent the issue by saying that developing custom extensions for a client doesn't involve distributing software?
The relevant part of the GPL:
You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License.
Cheers,
Nils
