There is an article on TechNet about the forest’s tombstone lifetime for Active Directory (http://technet.microsoft.com/en-us/library/cc784932(WS.10).aspx) that was discussed on an internal MSFT DS Team / MSFT MVP email list. The discussion pointed out that there is a little confusion around the article.
Specifically the confusion can come up around step 8
Note the value in the Value [...]