Despite the idea of dedicated teams, we really haven’t encountered much in the way of problems with rotating staff on and off Scrum projects in general. Sometimes people come on and off because they tend to specialize in something like UI design and are constantly called out on multiple projects. Other times the work on the project has changed focus or we need someone to start something new. And finally, sometimes someone is just getting burned out an needs a change.
On Scrum teams the main swapping out of resources that gets discussed is when one of the weaker team members is voted off the island for failing to meet any of their commitments. We’ve had that as well, but the majority of our swaps have been for more benign reasons. I have no idea if we’re typical, but rolling people off at releases tends to work really well, or at least at the end of Scrum.