When we did the port we found various leaks in the IDE that were made worse by Roslyn, so we decided to take the time and fix those leaks, and optimize our use of Roslyn.
We want to get your feedback on how well it works and to let us know what problems you are running into. Once we feel that there are no regressions, we will make this part of the default IDE.
While Roslyn is very powerful, this power comes with a memory consumption price tag. The Roslyn edition of Xamarin Studio will use more memory.
We are working to reduce Roslyn's and Xamarin Studio memory usage in future versions.