Virtual desktop users aren't always happy users, especially if their desktop isn't as fast as they're used to. In this video, Steve Damadeo talks about the most common questions his help desk gets about virtual desktop infrastructure.
The main concerns tend to be usability and speed. Virtual desktop performance can lag, especially when there is a greater distance between the user and where the virtual machine host actually lives.
Damadeo also discusses application delivery use cases. When you determine how to deliver an app to users, figure out what the rendering needs are and how it will be used. Are you going to deliver a full virtual desktop or specific apps to a mobile device? If so, consider which applications will work well on a mobile device; sometimes, for instance, data entry applications won't perform up to par.