After installing PowerShell 3 on a Windows Server 2008 R2 machine, I can't execute .ps1 scripts from the Windows Explorer context menu.
It seems the PS3 installer sets the Shell registry key to a wrong value. After manually setting the Shell registry key to the old, PS1, value, everything works fine again.
See here for a full discussion:
Please check and eventually fix if you see a flaw in the PS3 installation routine.