We made a tremendous amount of improvements in SQL Server Management Studio (SSMS) for SQL Server 2008. Some of them you can see, such as being able to add different columns in Object Explorer Details, and others you can't, such as the speed improvements for loading large sets of objects.
One of the features we added was a new T-SQL Debugger. I really like this tool and use it a lot - at first, I ended up using it a lot more than I wanted to. When we made this tool, we assigned it an icon. A green arrow icon. Right next to where you normally click to run a query, so....
Many times you end up running a query in a debugger session rather than what you really wanted. Here's how to fix it: Open SSMS, right-click in any blank space in the icon bar, and click "Customize" from the menu that pops up. While that menu is showing, left-click-and-drag the green arrow icon to the right - in my case, all the way to the right. Close out that little menu.
Now it will be where you don't hit it by mistake as often.