Does everyone know about SQL Profiler?
One of the most annoying parts of developing a database application is when the database does not do what you think it should. Often, it ends up that is because you are not telling it exactly what you think you are.
For those times, if you are a SQL Server user (or MSDE user with the client tools installed) you can use SQL Profiler. Briefly, SQL Profiler allows you to see a trace of what is actually being sent to the database. On more than one occasion, I discovered much to my horror that I in fact was not sending the parameter that I thought I was.
If you are a SQL Server user, familiarize yourself with SQL Profiler. It can be a lifesaver.