I use IPython/SymPy for the same purpose. It is nice to be able to do these calculations on my local machine, in stead of relying on an internet conection. Plus I get the powers of Python to back me up if I want to do anything more compilcated.
It's not nothing, however, that Wolfram Alpha works spectacularly well on a phone. The mobile app even has a very useful keyboard that has common math symbols. With mobile data, at any given time, I'm much more likely to have a computing device with an internet connection than I am to have one with a useable programming keyboard.
Not that I'm against the progression of these tools, far from it, I just think that wolfram alpha does a better job at math homework type problems for most people most of the time. If you have more complicated modeling/statistical/etc. work, then bring out the bigger guns.
I used the Wolfram Alpha iPad app in real-time during mathematics / statistics lectures to check the notes on the blackboard and to try out alternatives. Very useful in the classroom.
I see that some professors (not in my school though) publish they’re lecture notes as IPython notebooks. That is super clever and allows interactivity with the lecture material. I don’t know the mobile/tablet support of IPython notebook however.
