Mapping Center Answer:

The ESRI_Optimized style and serverstyle were released at version 9.2 and include a set of line and fill symbols that are designed for drawing performance (favoring speed over graphical quality). We recently wrote a technical article that details our performance testing of various kinds of symbols that you can create, showing which draw the fastest:

http://support.esri.com/index.cfm?fa=knowledgebase.techarticles.articleShow&d=33098

To get the serverstyle (which is a platform independent incarnation of a style), you would need to install ArcGIS Server. Otherwise, you just load the ESRI_Optimized in the style manager like any other style.