If I could ask for $1 every time someone asks me what I think about User Profile Disks (UPDs), I would be retired by now. Some time ago (maybe a long time ago), Eric (from XenApp Blog) and I were having a chat about how to deal with large user profiles due to some testing he was doing with Turbo Containers (by the way, a great tool for many use cases).
Interested on knowing what Microsoft was doing under the hood when UPDs were enabled within an RDS Session Collection, Toby Phipps, a Microsoft MVP for RDS, pointed me to Technet and showed me which commands could enable UPDs using the CLI. With that, Eric tested enabling UPDs within other platforms (i.e. Citrix Virtual Apps) and as expected, everything worked.
Fast forward to today, many people still do not understand what can and cannot be achieved with UPDs and how it compares to other similar technologies in the market. More than that, many still think this is a Microsoft-only technology/feature.