As part of my summer work with Sage, I've been porting a bunch of Maxima and Michael Wester calculus tests to Sage. Things started out kind of slow -- my 20kB/s Internet connection isn't good for much of any remote work -- but once I got Sage running locally through VMWare on a virtualized copy of Ubuntu Linux I was good to go. So far, I've ported all of the tests on integration and Taylor series as well as some on derivatives. Plus, I wrote my own series of tests for some of the basic rules of integration and derivation. Right now, I'm trying to diagnose why many of Maxima's tests fail on Sage, and I've discovered that the problem is often twofold. Currently, Sage has trouble with integrals that involve piecewise functions and/or additional variables inside functions with restricted domains, though we'll see what the future brings.
Next, I suppose that I'll either continue writing tests or maybe move on to creating the calc101 sort of website that I had envisioned for Sage. In any case, I'm having fun and learning a lot in the process!