I use Maple primarily in a Unix text window (TTY or "command-line" Maple), so I am used to seeing common subexpression labeling in the output of my computations. However, in Maple 11, GUI users don't see subexpression labeling by default.  I'll begin by talking about subexpression labeling as it appears in TTY Maple, then I'll talk about it in the GUI.

For starters lets look at an example in which a single subexpression is labeled:

I got an interesting question about integration yesterday. The question was about the integral of the rather innocuous looking function f := sqrt(1+sin(x)). The inside of the square root is always non-negative so the function is continuous (and bounded!) so it must have a continuous integral. The question I was asked, was if the following result was a bug in Maple: Int(sqrt(1+sin(x)),x) = (2*(sin(x)-1))*sqrt(1+sin(x))/cos(x) since the right-hand side is definitely not continuous at x=-Pi/2 + 2*n*Pi!