Hi there,
It would be awesome to have a Community folder within the Package Explorer in Studio, where community developers could share, rate and comment on custom activities. I believe that this would be a great way to accelerate the platform.
In order to avoid the spreading of malware and spyware, the developers could be forced to include the source code along with the activity, or the code could be made available through a decompiler such as this: http://ilspy.net/. In addition, the developers could be associated with trust certificates, so that the users don’t have to double check the source code of every activity.