Richard @ TechEd
I have just been to a session by Gert Drapers - Understanding and Optimising ADO.NET. I think of all the sessions I have been to at this year's TechEd, thus far, that this one will have most direct effect on the code I write.
If you use ADO.NET to access you SQL Server check out the session slides. The performance gains that are possibility available to you are significant, but I must dash to check my SQL query parameterization!