Security by isolation (VirtualBox), Tor-focused
Tor can be thought of like a secure proxy.
I experimented with it during my research on Replacing Firefox.
UPDATE: Tor has been subverted for some time.
I know when and how, with confirmation, but not by whom.
It must not be used for high-level security requirements (governmental, military, international) and probably even mid-level requirements (corporate, police). Little people using it as a proxy are fine.
Don't do anything illegal with it if you're within three degrees of a Bad Guy. So.. don't use it for anything illegal. Remember that PRISM records everything, so that, once flagged, you can be found retroactively guilty (even by association) for past internet usage.