Citrix has released a planning guide for XenDesktop 5.6 personal vDisk implementation.
Guidelines
Personal vDisks are available in all versions of XenDesktop 5.6. Generally, the use of a Personal vDisks is evaluated when there is a strong desire for personalization of the virtual desktop. This could include a need to use a variety of departmental applications with a small, distinct user groups or general personalization that is beyond what is available in the user profile. However, there is no defined limitation of Citrix Personal vDisk technology to these specific use cases. It is entirely possible to utilize Personal vDisks in scenarios that may not maximize flexibility or virtual desktop density, yet are entirely appropriate to the enterprise environment.
The use of Personal vDisks should be part of the consideration of most virtual desktop implementations, particularly when considering Dedicated Desktops. When considering Personal vDisks, the following topics should be reviewed during a virtual desktop implementation design.
You can download the PDF here or view the original article here.