I really wish I have known about these changes two years ago. So that I can save some hours for resolving a weird gacutil issue.

http://blogs.msdn.com/b/mjeelani/archive/2010/06/07/top-2-things-you-should-know-about-the-global-assembly-cache-gac-in-net-4-0.aspx

http://blogs.msdn.com/b/astebner/archive/2006/11/04/why-to-not-use-gacutil-exe-in-an-application-setup.aspx

http://blogs.iis.net/davcox/archive/2009/07/14/where-is-gacutil-exe.aspx

Hope this helps,

-Jack