Forum OpenACS Q&A: Re: Questions for community members who make a living working with OpenACS
Can such a business be run profitably - absolutely! We do so at Collaboraid. The important point here though is that the feasibility of your business will depend at least as much on your ability to find and build relationships with clients as on which particular web technology you happen to use.
Regarding licencing I really don't see the GPL as being any problem. Licensing-wise there are two types of customers, there are those who are committed to Open Source (MIT, Heidelberg, and Greenpeace come to mind) and there are others who prefer to keep their sources to themselves. Either way, the GPL poses no problem.