Hiya,
Well yes you could say that there are definately features worth charging for. The fact you can manage unlimited projects, assign tasks to collaborators, upload files to projects and submit invoices for those projects are all features that could be charged for. I don't think its right to take some features out for 'standard' users and only allow 'pro' users to use them because the features are dependent on each other in my opinion. So the best thing to do is limit the use, to say 10 projects and invoices.<p>Thanks for the comment.