> I just learned about this software from my mathematician son, and I think
> it looks like a pretty nice, well-developed system for symbolic math:

Have you seen wxMaxima?  It's an interface to Maxima, and I strongly
prefer it over Sage.  Sage is kind of a pain to set up because it runs
in a web browser.  Sage runs Maxima anyway for all of the heavy
lifting, so the performance will be about the same.

If you're just looking to try it out, you can always use the Sage
Online Notebook (http://www.sagenb.org/) to start.  Then you can
compare it with the easy-to-install wxMaxima (in the repos) and see if
Sage is worth the install. :)

-Max