What? Noone said SQL Server Profiler yet? How the heck do you guys find out what goes on behind the scenes without it? :-)

Especially good when you are after better performance. A quick profiler run will find those pesky SharePoint "specialities" in .NET like using foreach instead of for loops, or the difference in performance of doing SPContext.Current.List.ItemCount and SPContext.Current.List.Items.Count, finding deadlocks, timeouts etc