Okay, I've got tired of this UI, and I'm swamped with other tasks, but there is some money left from my travel to SotM. So I am announcing a grant: 100€ for a merged pull request allowing people to subscribe to comments in OSM user diaries. (NB: 300€ now, thanks to Stereo and Mikel.)
There should be a checked by default checkbox near the "Save" button ("Receive notifications about further comments"), and a button to subscribe/unsubscribe. All notifications should go to e-mail, much like changeset comments now.
When you have your pull request merged, I'll transfer that money to your card or bank account. And of course I'll publish a big thank you :)
The offer is not indefinite: the PR must be submitted until the 1st of November and merged before the 1st of December. And yes, there might be a competition, in that case OWG will decide the winner by merging a pull request.