You may have noticed that there is a new build of Revit 6.1 available for download at the Download Center. The build number for this build is 20040720_2100 and addresses the following issues:
1.. Some Sloped Ceilings would not display their grid/surface patterns - CORRECTED!
2.. Memory errors during large renderings and walkthroughs - CORRECTED!
3.. Issues with files with linked .dwg files which have had shared coordinates published to them - CORRECTED!
If you are not experiencing any of these issues, it is not necessary for you to download the latest build. If you plan on doing walkthroughs, large rendering, use sloped ceilings and/or use project coordinates, it may be worth your while to update your version of 6.1.