Why does Powershell take so long to init?

The Powershell team has a fix for this on their blog.

Content of the script from the site mentioned Update-gac.ps1

Set-Alias ngen (Join-Path ([System.Runtime.InteropServices.RuntimeEnvironment]::GetRuntimeDirectory()) ngen.exe)
[AppDomain]::CurrentDomain.GetAssemblies() |
    sort {Split-path $_.location -leaf} |
    %{
        $Name = (Split-Path $_.location -leaf)
        if ([System.Runtime.InteropServices.RuntimeEnvironment]::FromGlobalAccessCache($_))
        {
            Write-Host "Already GACed: $Name"
        }else
        {
            Write-Host -ForegroundColor Yellow "NGENing      : $Name"
            ngen $_.location | %{"`t$_"}
         }
      }