In all systems prior to Windows Server R2, if we delete the user by mistake, we can recover it because the user in the domain has a propertytombstonelifetime (tombstone life cycle), details:http://support.microsoft.com/kb/216993 , the recovery can be done as long as the data is recovered within the tombstone lifetime period. There are two commonly used tools when recovering:
1. LDP
2.ADRestore
Then there's a big problem when it comes to restoring the two tools: when you're done recovering, some of the properties of the recovered objects are lost! For example: passwords, attributes of the group to which they belong, and so on.
There is a new feature in window Server R2--------Active Directory Recycle Bin, and the Active Directory Recycle Bin feature is not enabled by default.
Improve functional Levels :
set-adforestmode –identity contoso.com - forestmode windows2008r2forest
open Recycle Bin :
Enable-ADOpti Onalfeature–identity "Recycle Bin Feature" –scope   forestorconfigurationset–target   "contoso.com"
Windows Server R2 Active Directory Recycle Bin