An ADO.NET multi-tier solution

This article is my own approach on how a multi-tier application could look like in C# and ADO.NET. The program has a GUI (Graphical User Interface), BO (Business Object) and DO (Data Object). Multi-tier is in my vision a program where the GUI doesn't have logic (no code that makes decisions), the DO only reads and save data to the database and all the rest is done by the BO. That's what I tried to accomplish with this code.

http://www.codeproject.com/cs/database/Multi-Tier.asp