Execution Policies
By default PowerShell can’t run scripts when first installed because the execution policy is set to Restricted. Lee Holmes has put a good explanation of some of the thinking around execution policies and what should be done about them - http://blogs.msdn.com/powershell/archive/2010/02/12/building-on-powershell-execution-policies.aspx
For more information see page 551 of Ed Wilson’s new book - Windows PowerShell 2.0 Best Practices – which I will be reviewing soon.