Ah yes, repeated spaces. Like you, I thought that it would work, however try the following code in the python window and in a feature class's label expression. Comparing the two you will see that it does not.
Python window:
def FindLabel():
x = "cats"
y = "dogs"
a = "cat"
b = "dog"
return x + " " + y + "\n" + a + " " + b
print FindLabel()
Python label expression:
def FindLabel():
x = "cats"
y = "dogs"
a = "cat"
b = "dog"
return x + " " + y + "\n" + a + " " + b
I would love to write a function that does the tab work for me, by reading the length of the string before it then applying spaces according to it's remainder of the length divided by 5. It's a lot of work but I would do it if I thought it would work. It won't because the python label expression interpreter seems to ignore repeated spaces.
I think this is another short coming of python label expressions that I imagine will get worked out in later versions - hopefully since we are discussing it here. Adding columns to labels is huge in my work, I've been wanting this feature for years.
Just curious, are folks getting a different behavior then I described running the above code?