Last year, I mentioned a trick about how to copy dll from GAC, but the approach is very inconvenient. Today I saw a really awesome artile Using Explorer to get to physical files in the GAC from Jeff Key.
The Explorer extension the framework installs to view the GAC in %windir%\assembly doesn't let you do much with those files. If you try to access the physical folders below the assembly folder, you are redirected to the assembly folder. If you want to get at those files (and if you do, be careful), simply subst a drive to the %windir%\assembly\gac folder.
For example, if I want my GAC files to be represented by drive letter G, I simply enter the following:
subst g: %windir%\assembly\gac
The subst.exe command allows you to substitute a folder on your computer for another drive letter, it's a very useful DOS command, and you can use "subst g: /D" to remove the virtual disk.