• Get-Counter can now return counters that contain an apostrophe character in French editions of Windows.
• You can now view the GetType method on deserialized objects.
• #Requires statements now let users require Administrator access rights, if needed.
• The Import-Csv cmdlet now ignores blank lines.
• A problem where Windows PowerShell ISE uses too much memory when you are running an Invoke-WebRequest command has been fixed.
• Get-Module now displays module versions in a Version column.
• Remove-Item –Recurse now removes items from subfolders as expected.
• A UserName property has been added to Get-Process output objects.
• The Invoke-RestMethod cmdlet now returns all available results.
• Add-Member now takes effect on hashtables, even if the hashtables have not yet been accessed.
• Select-Object –Expand no longer fails or generates an exception if the value of the property is null or empty.
• Get-Process can now be used in a pipeline with other commands that get the ComputerName property from objects.
• ConvertTo-Json and ConvertFrom-Json can now accept terms within double quotes, and its error messages are now localizable.
• Get-Job now returns any completed scheduled jobs, even in new sessions.
• Issues with mounting and unmounting VHDs by using the FileSystem provider in Windows PowerShell 4.0 have been fixed. Windows PowerShell is now able to detect new drives when they are mounted in the same session.
• You no longer need to explicitly load ScheduledJob or Workflow modules to work with their job types.
• Performance improvements have been made to the process of importing workflows that define nested workflows; this process is now faster.

Source: http://technet.microsoft.com/library/hh857339.aspx#BKMK_bugs