http://social.technet.microsoft.com/Forums/en-US/category/appvirtualization

Microsoft's App-V section within Technet is the most frequently used place to get answers by community members and by Microsoft employees. Due to the amount of users and experts its the forum with the highest update frequency.

http://www.appvirtguru.com

While AppVirtGuru has less readers and posters than Technet, the "perceived quality" is somewhat higher. Often, answers are very detailed.

AppVirtGuru also covers other Application Virtualization technologies.

DSGUG is the most popular German App-V related forum.