— Tyler (2006-07-07 22:27)
This is commonly done with shareware. But I assert that it's not a good idea with open-source, free software.
Why not? Because, quite simply, it will tick off your customers.
Also, your open-source community will just develop their own free versions of whatever features are in your "pro version". And then you will be competing with your own community / userbase, when it would be much better for you to be cooperating with them. Competing with your customers is sure to create/be a conflict of interest and will cause you to lose credibility (and along with that customers).