I have always been a great fan of the SOS.dll debugger extensions. It provides huge help in just so many situations, where a deep look into the inner state of the CLR is needed at runtime and the common debugging tools of Visual Studio simply dont go far enough. When working on the new memory management of ILNumerics SOS many times lived up to its name and allowed the final insight needed to make it work. How I wished, the processor itself would expose similar potential to find out ‘what’s going on’ as the CLR does …!
Tess’ blogpost about new commands in SOS for CLR 4.0 therefore triggered great expectations here. So I finally managed to take a quick look onto it:
!help already seems to come up with a whole lot of much more commands than before. In the past I have been using a small subset only, mainly !GCRoot, !DumpHeap, !DumpObject and !DumpClass. Some of the newly appeared commands sound promising as well: !HeapStat, !ListNearObj, !AnalyzeOOM, !HistInit, !HistObj, !HisttObjFind, !HistRoot, !ThreadState,!FindRoots, !GCWhere and !VerifyObj.
Wow! GCWhere, FindRoots and those Hist??? command definitely deserve a closer look in one of our next programming sessions – even if the next GC issue is not very lickely to appear for ILNumerics really soon 
I have not been able to find part II of Tess’ blog post, but luckily the msdn documentation is still there for those commands.
Strange: between all those reputable commands one is found called ‘!FAQ’. I tried to find out, which answers the users of the SOS might seek most intensively. But unfortunately, it didn’t work out:
!FAQ
The name 'FAQ' does not exist in the current context
??
@Update: Somehow I really have missed the fact, that nowadays, everybody seem to be using a new tool, superseding the SOS.dll: Psscor4…. Anyway, those commands will nevertheless be checked in there. 