I ran into an issue the other day where we had two servers in an isolated domain that were steadily losing disk space to an unknown cause.  It turns out the cause was Forefront Client Security.  The reason?  Forefront's history kept accumulating events at a rate of approximately 120 events every five minutes!  The history folder grew to about 2.5 GB in just over three weeks and had tens to hundreds of thousands of files (not sure how many exactly as Explorer would crash before I could get a count).  Why?  Group Policy was set to "Process even if Group Policy object have not changed" and so the firewall rules set up policy were being reevaluated by FCS every five minutes!  Not a bug, persay, but definitely something that should be addressed in future versions of FCS.  Anyway, here's a link to the newsgroup article I posted on TechNet.  No responses yet at the time of this blog post, but hopefully somebody at Microsoft will chime in on this issue.  http://forums.microsoft.com/ForeFront/ShowPost.aspx?PostID=2258749&SiteID=41&mode=1