Dear Jeremy:

This morning I became aware of the events of this past weekend when we had the unfortunate failure of our network server. I want to thank you for spending many hours in the office on Saturday and Sunday in order to correct the problem so that our department could be fully functioning on Monday morning. I have been very impressed with your technical skill and dedication in the past, but your efforts this weekend were exemplary and serve as an important reminder of how fortunate we are to have you as a member of our team. Thank you for your dedication and commitment. 

Sincerely,
Dough Staintent