I've been pondering this a lot. Here's my current thinking...
I personally miss the "xxx commented". "Somebody" just doesn't convey enough info.
Putting the number inside the brackets makes it harder to filter with mail filters.
So here's my plan - I'm right now adding plugin hooks to the enotify function. I'd like to put back the names by default.
And threading these based on references: works on "real" mail readers. It seems only gmail ignores the threading headers and forces a subject line match.
So I propose a plugin which can alter the subject line in the notify emails either for privacy or for Gmail threading or both.
Also Simon I believe the issue with the privacy of the subject line is that these are visible on your mail reader screen even if the message isn't selected. It's like the N-S-F-W plugin - there are times when you might not want to have the names of certain people appearing on your screen and we should accommodate this. But "somebody did something" doesn't seem very informative and it shouldn't be the default.
@Mike, the "xxx commented", when properly threaded, is really more pleasant than "somebody commented" (I tested it in Thunderbird). The other way, to have ALL comments by one person threaded together on GMail is making some "conversations" (threads) to have more than 50 messages (and growing). So, I agree with you. Default to "xxx commented" and plugin to "Somebody commented".