I've been using Sympy in the past few weeks more than ever before, and I have to say it's been quite a nice experience.
As a an almost-newcomer, the single most annoying thing was that you can't copy-and-paste code from the website. Every time I select code from the documentation on [1], the live shell opens with seemingly unrelated code ("I didn't ask for this!"), and after hiding it, I find myself on another place in the documentation. Yikes!
Other than that great work. I particularly appreciate the helpfulness of this "mailing list".
Cheers,
Nico