Permanently modify an environmental variable from PowerShell

For instance, here we are adding to the PATH.

PS> $addMe = "C:\utilities";  
PS> [Environment]::SetEnvironmentVariable("PATH", $env:Path + ";" + $addMe, [System.EnvironmentVariableTarget]::Machine);  

This also works for variables other than PATH and for additional scopes:

[System.EnvironmentVariableTarget]::Process
[System.EnvironmentVariableTarget]::User
[System.EnvironmentVariableTarget]::System