Whoever designed the Script Debugger's Step Into and Step Out buttons putting them smack dab against each other probably didn't use it much. The close proximity has lead to many an error by myself. If you use the debugger, you frequently click the Step Info button a bunch of times in a row to step through a script (not unusual to do 30 or 50 clicks). However, if your mouse ever so gently slides to the right even a few pixels, you can accidentally click the Step Out button and your debugging is off to the races! This is a poor UI design for people who do much debugging of script. It doesn't matter if the mouse slides to the left much because the Step Over button is so similar in function to Step Into. It does not have near the danger as the Step Out button.
Here is the graphic of the tool bar and the Step Into is the one with the arrow down and the Step Out is the one with the arrow up. There isn't even a pixel between them. The run and stop buttons are separated with a nice space to the Step buttons. It would be really nice to put that same amount of space between the Step Into and Step Out buttons to avoid this frequent and easy to do pitfall.
Hopefully FMI will separate those two buttons by a bit more space, especially since space is not a premium on the debugging bar.