This is one of those "how in the world did I not know this?" nuggets. During a code review yesterday, one of my colleagues asked me to make an LED bigger on the panel of a VI. After my resize attempt, the LED was oval-shaped, to which my colleague remarked, "You know, you can shift-drag to resize objects proportionally in both directions".
How cool is that? From what I can tell, you can do a shift-drag-resize on any object that can resize in multiple directions, including objects on the block diagram. Remember this nugget whenever you're resizing an object and you want it to keep the original height/width ratio at its new size.