Yes (to lakerat), as far as I can tell, my site/shell account haven't been hacked. So, that aside, the problem looked backup/restore related to me, and the incident I cited seemed the best available candidate (you know, kind of like the republican party's situation:). But in that case, I'd have expected other people to report the same experience. And nobody has, so far. So I'm less convinced of my initial guess, but can't dream up any alternative. If you assume no hack, how do you otherwise account for all permissions, on every single file everywhere (web and "offline" files), changed to 755? Note that that's not group/world writable, and at best lets people read previously-600 files (of which I have many). And no files seem missing or "damaged" in any way, as far as I can tell (by diff'ing them against tarball backups that I periodically make and download to my soho lan). So my best (and only available) guess is still that it's gotta be some kind of dreamhost foul-up of some kind. And, by the way, this time they haven't replied to my email at all, though on several previous occasions they've been very prompt, courteous and helpful about replying.
And, vis-a-vis bobcat's shell remarks, I'm a professional Unix C programmer (for decades, see my resume at http://www.forkosh.com/resume.html) and probably didn't "screw things up" myself, although, of course, anything's possible (i.e., during those decades I've indeed taken ample advantage of many opportunities to screw things up:).