DateTime.FromFileTime
should do the trick:
PS C:\> [datetime]::FromFileTime(129948127853609000)
Monday, October 15, 2012 3:13:05 PM
Then depending on how you want to format it, check out standard and custom datetime format strings.
PS C:\> [datetime]::FromFileTime(129948127853609000).ToString('d MMMM')
15 October
PS C:\> [datetime]::FromFileTime(129948127853609000).ToString('g')
10/15/2012 3:13 PM
If you want to integrate this into your one-liner, change your select
statement to this:
... | Select Name, manager, @{N='LastLogon'; E={[DateTime]::FromFileTime($_.LastLogon)}} | ...