When .net Framework 4.0 release it comes with one major change and that change is GAC (Global assembly cache) location. Since first version of .net framework release GAC location is fix to %windir%/assembly. This is default location and you can change that location but default installation is always point to above location . ( If you want to know how to change GAC Location manually then look at my post http://dotnetstep.in/change-the-location-of-gac
In .net 4.0 this default location is change to C:\Windows\Microsoft.net\Assembly
Why this thing is important to know?
1. As default location is C:\Windows\Assembly we used to drag and drop assembly directly to GAC but this is not the case when work with 4.0
2. It is better to use GACUtil tool for .net 4.0 to install assembly.
Following link contain many information regarding this.
It would be nice if C:\Windows\Microsoft.net\Assembly as same look and feel as older GAC.
as per msdn shell extension is obsolete (http://msdn.microsoft.com/en-us/library/34149zk3.aspx)
Please provide your input if you have any other thing to add.