Hi all. I'm one of the Tor authors.
We're trying very hard to get out the message that you should always use encrypted protocols over Tor, if you're doing anything even slightly sensitive.
Right now, we do this in our documentation, and in a list of warnings on our download page. But obviously, this isn't good enough, since some of the commenters here seem to be surprised at finding it out.
Does anybody have good ideas about how to get the word out better?
(As for the SSL MITM thing: we've run into situations like this one before. Usually, it turns out that the exit node isn't doing the MITM itself, but is getting MITMd itself by its upstream. This happens depressingly often in some countries, and in some dormitories. I've dropped a line to the directory authority operators Mike Perry (the guy who maintains the Torbutton firefox plugin) has been working on an automated detection tool for this stuff. It would be great if somebody with programming chops would step up and give him a hand.)