I know you can copy/paste the URL bar to save a permalink for a message thread. Is there a way to permalink a specific message within a thread?
If Gmail is in "conversation view on", which you can change on the settings page, it will always thread the conversation. It appears to take the message ID, and weave it back into the proper conversation.
So even if you turn off conversation mode, then copy the url, then turn it back on, you will see the entire conversation. It doesn't appear to even expand the message of interest.