The Application Compatibility Toolkit allows you to specify which compatibility information you share based on the application tested. So for example if you have compatibility information for bespoke, home grown applications that you don't want to share with the online community you can choose not to do so.
To configure which application compatibility information you share with the online community, do the following:
Before kicking off the Send/Receive process, click the View the specific applications to be shared with the ACT Community link in the Confirm dialog box, and then deselect any applications that you don't want to send.
For more information on ACT check out my page in the Deployment Den: http://blogs.technet.com/james/pages/application-compatibility-toolkit-5-0-act.aspx