I have long waited for this feature as I got used to Visual Studio's debugging feature where you can simply put a breakpoint beside a code line and hit the debug button. SQL Server Management Studio now has a Debug button together with the Execute button (except that in Visual Studio, your F5 key would be your Debug command whereas in SQL Server, that would be the Run/Execute command).
This will allow you to step over your code - whether it is calling a stored procedure or a TSQL script - and step thru it a line at a time or at one shot. You can even step thru nested calls, like calling a stored procedure that calls another stored procedure. It will open up a new tab displaying the codes for the procedure or function that you are calling from your TSQL code. I'm just glad it's already in RC0. Check out my video from BlogCastRepository.com on how this works