I’m one of the founders and writers over at PowerShellTaskForce.com and during the last week I have published two articles about how to monitor Active Directory from PowerShell using both pull and push methods. Head over there and read the articles:

http://powershelltaskforce.com/2013/11/monitor-changes-in-activedirectory-part-1/
http://powershelltaskforce.com/2013/11/monitor-changes-in-activedirectory-part-2/