I just moved a blog post out of the threads site and onto its own site so I can continue to edit it. The original location redirects to the new one via a redirect node. It works beautifully except for one thing: we lose the Disqus comments thread because the URL changed. This happens to us all the time, but it is preventable.
Our IDs are the result of concatenating the creation date with the pgfnum attributes of the node being rendered.
We do not generate IDs for anything posted before today. They already have threads, and to give them IDs would effectively delete their threads.
Here's a thread I started to test the feature. I kept changing its address and the comments didn't disappear. In fact I think they've dealt with the issue of existing threads getting IDs. But I'm still not generating them for nodes that were created before today, just to play it safe.