This discussion has been going for many years now and at times has almost reached epic proportions due to the conflicting information available from Microsoft. Recently the SBS MVPs were in a conference with the SBS CSS team and we raised just how confusing this was for the average person. In response one of the leads for the CSS team – Mark Stanfill has posted the “definitive” answer for us. Long story short is that by and large, you should NOT use the /3GB switch unless you are experiencing very specific messages in the event log. Check out their post here http://blogs.technet.com/sbs/ for more information.