There are times when adding validation logic can't be done purely by looking at individual insert/update/delete operations - and instead you want to be able to look at the entire change list of operations that are occurring for a transaction. 

Starting with Beta2 of .NET 3.5, LINQ to SQL now enables you to get access to this change list by calling the public DataContext.GetChangeList() method.  This will return back a ChangeList object that exposes collections of each addition, removal and modification that has been made. 

One approach you can optionally employ for advanced scenarios is to sub-class the DataContext class and override its SubmitChange() method.  You can then retrieve the ChangeList() for the update operation and perform any custom validation you want prior to executing it:

Figure 17

The above scenario is a somewhat advanced one - but it is nice to know that you always have the ability to drop-down and take advantage of it if needed.