We have been experimenting with LINQ to SQL on a couple projects lately and I am constantly impressed. I'll post some tidbits as I come across some neat features.
Today I had to display the last 4 digits of a customer's credit card number on the UI. I already have a DBML file in my project and the Customer table has been added to the designer. Customer has a CreditCardNumber property (ignoring encryption for purposes of this example). Of course business logic layers aren't new but all too often, you would find logic in the UI that displays the right 4-digits. But now implementing the BLL is even easier by simply implementing a partial class.
Partial Public Class Customer
Public Readonly Property Last4 as String
Return Right(Me.CreditCardNumber, 4)
You can take it one step further and override the CreditCardNumber property and change the Get to return ************XXXX instead of the clear text credit card number, which will make your business logic even more secure.