Question: I need to understand the fine details, possibilities and pricing of Salesforce OEM model. I can't find an official link about this on salesforce and google, only link available is this 2008 pdf : <http://www.developerforce.com/tdf/2008/april/Force_ISV_Partner.pdf>

Please share any good post/article on this.

Answer: 
We have done this using a simple validation rule on the oppty object, this checks if the Close date is 90 days old, and if true on the oppty status [Closed, Closed Won, whatever] - returns an error.

```
AND( 
OR(ISPICKVAL(PRIORVALUE(StageName),"Selected - PO Received"), 
ISPICKVAL(PRIORVALUE(StageName),"Closed Won")), 
CloseDate + 90 < TODAY() 
)

```

Off course, you can add the profile check as well (we use the administrator profile ID for allowing changes)

```
NOT ($Profile.Id = "00e20000004456")

```

Always remember to [tune your query](http://beginner-sql-tutorial.com/sql-query-tuning.htm) as much as possible for better performance.
I have used this syntax in a validation which has seemed to work well.

```
PRIORVALUE(LastModifiedDate) <> NOW()

```