We held off on upgrading for about six months, primarily because our IT department didn't want to support multiple versions. (It wasn't realistic for everyone to upgrade at the same time.) Plus, each new version of SolidWorks tends to be more resource-intensive, so companies that prefer to hold onto computer equipment as long as possible (like mine) have lots of incentive not to upgrade. Shortly after we upgraded to 2005, we had major crashing problems. The main reasons were outdated computer equipment, insufficient RAM and registry corruption. (SBaugh's FAQ about properly uninstalling SolidWorks came in very handy for that one.)