Yes, this weekend is their first time being open to public. My profile emptied also. It sort of comes and goes. I don't think it's permanent; just hard hit this weekend (I get the impression there were browser specific issues they are also having to fix, so maybe their closed group testing prior going public didn't see a lot of devices/browsers or have a big enough pool of testers to test being swamped with data all at once).
Many thanks for the responses, everyone! Clearly it's not just me. :-) I knew that leafmarks was new, but hadn't quite grasped *how* new. What I've seen so far looks promising, and the import worked like a charm. I guess I'll just sit tight and see what develops.