NiceVS performs several operations to make it nicer.
When you install this extension a dialog appears during next start of Visual Studio where you can chose which operations to perform. You can also chose not to display the dialog again. You can always change settings in Tools | Options | Environment \ NiceVS.
In previous versions the run-time replacement module was buggy and caused Visual Studio to crash. If you experience increased number of Visual Studio crashes or slow-down try disabling this module, and report the problem here on Sourceforge.
(Last updated for version 0.9.0)