MSH is Microsoft's new shell - and it has been developed in managed code. Because it is managed and large, it needs to be JITed each time it is run and this takes time. To speed it up, you can do a native generation by running the following command:
C:\windows\Microsoft.NET\Framework\v2.0.50215\ngen install "c:\Program Files\Microsoft Command Shell\msh.exe"
You may need to adjust this for folder names on your system (and despite how it looks here on Blogger, it is all one line!). On my laptop, this took startup from around 2-3 seconds to near instant. This is a beta performance issue (not having msh.exe ngened) that will get fixed for RTM, but for not, it makes startup faster.