Anthony/Helen, I don't know if either of you read the developer chat discussion that preceded me filing this feature request. http://moodle.org/mod/cvsadmin/view.php?conversationid=2805#c123849
The situation where it would be very helpful to let people delete their own attachments is when a developer is uploading a patch - or more to the point when they have already uploaded one patch, and then need to upload a revised version. Rinse and repeat a few times, and you end up with a bug with half a dozen patches and it is just a pain to work out which one(s) are still relevant. In this case it would be much better to let developers manage their own patches.
After I had filed this bug, this thing came up in a discussion with Dan http://moodle.org/mod/cvsadmin/view.php?conversationid=2806#c124196 - and I ended up deleting some useless attachments for him.
I had not thought of the use case of people uploading private information then wanting to delete it. That is a good one. however, I am not proposing to let all users do this, just people in the developers group.
I think the benefits of keeping the attachment lists cleaner so we can focus on what is relevant far out-way the tiny risk that people will use this to cause problems be deleting stuff they uploaded themselves.
Added some relevant watchers. I don't know if this is a good idea or not. It's just a thought.