Echo has finally gone belly up altogether -- is asking me for money in order to continue using the system.
For the time being I've reinstated Blogger, and will switch over to Disqus. All old comments are archived but are currently not searchable from their original posts. I'll try to fix that problem as soon as I can.
EDIT: OK, I'm switched to Disqus.
If anyone can make heads or tails of these instructions and could help me actually use them to repopulate Disqus with my old Haloscan comments (in one XML file containing all comments), I will pay them in monetary units to do so, since the alternative is to pay Echo, which I refuse to do on principle.