I am working in the same lab I came in at. We have 40+ students and I don't know anyone that has switched labs during a degree program (a few that have between their master's and PhD). The good thing is in our 6000 level classes there is usually a lab project of some kind that allows you to research another aspect of the field. You can also do special projects with a professor of your choice, for credit. Our school also has an agreement with the University of Ghent, Karl Franzenzs Univ, and another school in France that allows a semester or summer research programs.
Personally, I don't have the desire to switch labs. I would like to do something different if I go on for a PhD, but for my MS I'm fine with only one lab. I was looking for 2 things: a productive faculty and one of those faculty that were doing research I find interesting. Two years isn't a lot of time....